Notes to Consolidated Financial Statements (continued) 2. Available-for-Sale Securities 3. Property and Equipment 4. Sponsored Research and License Agreements 5. Agreement with Aventis SA The following is a summary of our available-for-sale securities at December 31 (in thousands): The estimated fair value of available-for-sale securities at December 31, 2001 was $104.8 million, with $5.8 million maturing within 1 year and $98.9 million maturing between 1 to 3 years. Gross realized gains on sales of marketable securities were $149,000 for the year ended December 31, 2001. Gross realized gains or losses were immaterial for the years ended December 31, 2000 and 1999. Property and equipment consisted of the following at December 31 (in thousands): At December 31, 2001, the annual aggregate commitments  we have under these agreements, including minimum license payments, are as follows (in thousands): After 2006, we must make annual payments aggregating $329,000 per year to maintain certain licenses. Certain licenses provide for the payment of royalties by us on future product sales, if any. In addition, in order to maintain these licenses and other rights during product development, we must comply with various conditions including the payment of patent related costs and obtaining additional equity investments. We have entered into various agreements with research insti- tutions, universities, and other entities for the performance of research and development activities and for the acquisition of licenses related to those activities. Expenses under these agreements totaled $1.6 million, $1.5 million and $1.3 million in the years ended December 31, 2001, 2000 and 1999, respectively. Depreciation and amortization expense was $272,000, $196,000 and $174,000 for the years ended December 31, 2001, 2000 and 1999, respectively. In 1997, we entered into an exclusive license agreement  with Aventis SA (formerly Hoechst Marion Roussel, Inc.). The agreement gave us a worldwide license to the patent rights and know-how related to the antipsychotic agent iloperidone, including the ability to develop, use, sublicense, manufacture and sell products and processes claimed in the patent rights. We are required to make additional benchmark payments  as specific milestones are met. Upon commercialization of  the product, the license agreement provides that we will pay royalties based on net sales. Twenty-Four 2001 2000 Furniture and office equipment $ 290 $ 191 Leasehold improvements 229 213 Laboratory equipment 363 354 Computer equipment 380 250 1,262 1,008 Less accumulated depreciation  and amortization (687) (415) Property and equipment, net $ 575 $ 593 2002 $1,596 2003 329 2004 329 2005 329 2006 329 $2,912 2001 2000 Amortized Unrealized Amortized Unrealized Cost Gains Fair Value Cost Gains Fair Value Money market funds $ 5,478 $ — $ 5,478 $ 17,835 $ — $ 17,835 Securities of the U.S. government and its agencies 60,785 1,380 62,165 52,280 393 52,673 Corporate notes and bonds 36,603 511 37,114 42,289 296 42,585 Commercial paper — — — 3,957 2 3,959 $102,866 $1,891 $104,757 $116,361 $691 $117,052 Classified as: Cash equivalents $ 5,478 $ 19,829 Marketable securities 99,279 97,223 $104,757 $117,052