CYTOKINETICS AND GLAXOSMITHKLINE AMEND COLLABORATION AGREEMENT FOR SB-743921 Maturation of Cytokinetics' Capabilities Enables Increased Responsibility for Clinical Development under Augmented Development Program for KSP Inhibitors

Exhibit 99.1

CYTOKINETICS AND GLAXOSMITHKLINE AMEND COLLABORATION AGREEMENT FOR SB-743921

Maturation of Cytokinetics’ Capabilities Enables Increased Responsibility
for Clinical Development under Augmented Development Program for KSP Inhibitors

South San Francisco, CA, September 27, 2005 — Cytokinetics, Incorporated (Nasdaq: CYTK) announced the amendment of the company’s strategic alliance with GlaxoSmithKline (GSK), which will provide Cytokinetics an expanded role in clinical research and development for SB-743921, a novel, small molecule inhibitor of kinesin spindle protein (KSP). This drug candidate is being developed under an alliance focused on novel small molecule therapeutics targeting human mitotic kinesins for applications in the treatment of cancer and other diseases.

Under the terms of the amendment, Cytokinetics will lead and fund development activities to explore the potential application of SB-743921 for the treatment of non-Hodgkin’s lymphoma, Hodgkin’s lymphoma and multiple myeloma, subject to the option for GSK to resume responsibility for development and commercialization activities for SB-743921 for these indications during a defined period. Cytokinetics’ development activities will be conducted in parallel with GSK’s conduct of development activities for SB-743921 in other indications and for ispinesib (SB-715992). Ispinesib is the first drug candidate to emerge from the strategic alliance and is currently the subject of a broad clinical trials program pursuant to the alliance.

The amendment provides for acceleration of the formation of a Joint Development Committee to oversee the conduct of all development activities conducted by Cytokinetics and GSK for SB-743921 and for the exercise of Cytokinetics’ option to co-fund certain later stage development costs for this drug candidate. In addition to the payments that GSK may make to Cytokinetics under the original terms of the collaboration agreement, based on Cytokinetics’ expanded role under the amendment in the development of SB-743921, Cytokinetics may receive additional pre-commercialization payments from GSK based on the achievement of certain milestones for SB-743921 for the additional indications described above and increased royalties from GSK on net sales of products containing SB-743921 under certain scenarios.

“The expanded role to be played by Cytokinetics in the joint development of SB-743921 with GSK reflects the maturation of Cytokinetics’ capabilities in the area of clinical research and development since the initiation of the collaboration in June 2001,” stated Robert I. Blum, Executive Vice President, Corporate Development and Commercial Operations and Chief Business Officer. “We have evolved as a company, increasing the resources that we can bring to bear on development activities now being directed to this program. We look forward to the initiation of a clinical trial for SB-743921 in non-Hodgkin’s lymphoma in the coming months.”

SB-743921 entered a Phase I clinical trial conducted by GSK in the United States in May 2004 to evaluate its tolerability and pharmacokinetics in advanced cancer patients. Data relating to SB-743921 were presented at the 2005 Annual Meeting of the American Society of Clinical Oncology in May 2005. The data presented were from 20 patients that collectively had a variety of advanced solid tumors and received doses of SB-743921 intravenously once every 21 days. SB-743921 appears to have an acceptable tolerability profile for patients suffering from advanced solid tumors. The dose-limiting toxicities observed to date are prolonged neutropenia, febrile neutropenia (with or without infection), elevated transaminases, hyperbilirubinemia and hyponatremia. Notably, neurotoxicities, mucositis, thrombocytopenia, alopecia and nausea/vomiting requiring pre-medication have not been observed to date.

“We are excited about investigating new potential therapeutic indications for SB-743921, augmenting the efforts of our partner in evaluating KSP inhibitors for their potential in the treatment of patients with various cancers,” stated Andrew A. Wolff, M.D., F.A.C.C., Senior Vice President, Clinical Research and Development and Chief Medical Officer. “Our working in parallel with GSK in development of SB-743921 is consistent with the original intent of our alliance to explore the full breadth of the therapeutic potential of our drug candidates. SB-743921 is the second KSP inhibitor to enter clinical trials under our collaboration and has distinct clinical potential that we believe warrants exploration in additional tumor types.”

Cytokinetics Joint Development of SB-743921 Announcement
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Research & Development Expense Guidance for 2005

The financial impact of this amendment will not result in an increase in Cytokinetics’ research and development expense guidance for 2005. The guidance previously provided for research and development expenses for 2005 is $45 to $49 million.

Conference Call / Webcast

Cytokinetics will host a conference call on Tuesday, September 27, 2005 at 6:00 p.m. Eastern Time. The conference call will be simultaneously webcast and will be accessible in t