We investigated the effects of taxol, an antimicrotubule agent active in different cancers, on the human NCI-H295 steroid-secreting adrenocortical carcinoma cell line. Cells were incubated for 48, 72 or 96 h with taxol 10(-10)-10(-4) M. Cell viability was evaluated by MTT assay with IC50 calculation. Apoptosis was investigated by measuring DNA fragmentation with ELISA assay after cell exposure to taxol at IC50 for 24 h. For secretion studies, aldosterone, cortisol, testosterone and dehydroepiandrosterone-sulphate (DHEA-S) were measured by RIA in the conditioned medium after 96 h exposure to taxol 10(-10)-10(-6) M, and expressed as percentage of steroid production by control cells. By MTT, taxol induced a dose-dependent inhibition of cell proliferation, with ICs50 at 72-96 h corresponding to blood levels achieved in vivo in patients with other types of cancer. Nuclear fragmentation, morphologically confirmed at electron microscopy, showed a 4-fold increase after exposure to taxol. With 10(-6) M taxol, aldosterone decreased to 48%, cortisol to 61%, testosterone to 76% and DHEA-S to 89% of steroid production by control cells. Taxol is an effective cytotoxic and antiproliferative agent in a human adrenocortical steroid-secreting carcinoma cell line. Apoptosis induced by the drug is involved in neoplastic cell death.