With the use of clonogenic survival assays, we show that wild-type p53-expressing A2780 human ovarian cell lines transfected with a dominant negative mutant p53 gene (codon 143, valine to alanine) acquired cross-resistance to ionizing radiation, cisplatin, doxorubicin, and 1-beta-D-arabinofuranosylcytosine. However, these mutant p53-transfected cell lines retained sensitivity to taxol and camptothecin. We also show that immature thymocytes from mice with the p53 gene genetically inactivated showed reduced ability to undergo apoptosis after treatment with ionizing radiation and cisplatin compared with wild-type mice. However, taxol-induced apoptosis in thymocytes does not seem to be dependent on p53 status. Camptothecin also induced apoptosis in a p53-independent manner in thymocytes at low doses but in a p53-dependent manner at high doses. These data suggest that taxoids and camptothecin analogs could have activity in tumors that have aberrant p53 function and provide a rationale for the clinical observations of responsiveness of refractory ovarian cancer to these drugs.