Updated from 10:18 a.m. ESTLess than one week after its chairman said his company wasn't looking to make a big acquisition just to boost its stock, Amgen ( AMGN) said Monday it would spend $1.3 billion to purchase all of the shares it doesn't own in Tularik ( TLRK). In late afternoon trading, Amgen's stock gained $1.73, or 3%, to $59.82, an encouraging sign because acquirers' shares often drop in reaction to their takeover bids. Amgen, of Thousand Oaks, Calif., now owns 21% of the shares in Tularik, a South San Francisco-based biotech company. The deal places a value of $25 a share on Tularik's stock, which closed at $17 on Friday. In Monday trading, Tularik's shares jumped $7.56 to $24.56, reflecting the offer price's rich premium. Amgen said the transaction won't affect its 2004 financial guidance for what it calls adjusted earnings per share of $2.30 to $2.40, which was announced in late December. The guidance for earnings based on generally accepted accounting principles (GAAP) is $2.13 to $2.23; but Amgen added that it has yet to calculate the one-time expense associated with writing off certain research and development activities associated with the Tularik acquisition. The companies said the deal is expected to close during the second half of 2004. The transaction, approved by the boards of both companies, must be approved by Tularik's shareholders as well as by regulators. Tularik is a company with no products and a tiny amount of revenue from licensing and research agreements, but Amgen is betting that it has a lot of promise. Tularik has five products in various stages of clinical testing, the most advanced being a liver cancer drug called T67 that is in Phase 3 testing, the last stage prior to a company seeking approval for a drug from the Food and Drug Administration. Other experimental Tularik drugs focus on cancer of the esophagus and stomach; rheumatoid arthritis and psoriasis; diabetes; and obesity. Amgen and Tularik have been collaborating on cancer drug research. David V. Goeddel, Tularik's chief executive, will remain with Amgen, overseeing research projects from his South San Francisco office. Approximately 300 of Tularik's research scientists will join Amgen.