Taxol is the first of a novel class of anticancer drugs, the taxanes. Taxol's unique effects include its ability to polymerize tubulin into stable microtubules in the absence of cofactors and to induce the formation of stable microtubule bundles. During its development, formidable challenges were overcome: a suitable formulation was developed, an adequate supply was ensured, severe hypersensitivity reactions were diminished in incidence and severity, and clinical efficacy was demonstrated. Phase II evaluation is still underway; to date, clinical efficacy has been demonstrated in ovarian, breast, non-small-cell lung, and head and neck cancer. Response rates were low in early studies in melanoma, prostate, colon, cervix, and renal cancer, but for these tumors, additional evaluation is ongoing with a higher Taxol dose or different schedule. In December 1992, Food and Drug Administration approval was granted for use of Taxol as second-line therapy in ovarian cancer patients. Nevertheless, important questions regarding optimal use of this important new drug remain. These include determination of optimal dose and schedule and development of suitable combination chemotherapy regimens. The clinical development of Taxol and current status of phase I, II, and III clinical trials are reviewed.