The direct effects of gossypol on the serum-free primary cultures of rat luteal cells and cytotrophoblasts were observed. The results indicate that: (1) Gossypol affected the viability of the cultured rat luteal cells, LD50: 1.6 (0.4-2.9) micrograms.ml-1. (2) The basal secretions of progesterone were significantly inhibited at low and high concentrations. The activities of 3 beta-HSD, adenyl cyclase and hCG-stimulated progesterone production were inhibited by higher concentrations of gossypol. (3) Gossypol damaged cultured human decidual cells and cytotrophoblasts, the LD50 were 3.5(0.4-6.6) micrograms.ml-1 and 4.1(0.6-7.6) micrograms.ml-1, respectively. These results suggest that the luteolytic effect is the main mechanism of action for the termination of early pregnancy by gossypol, while the direct damaging effects on decidual cells and cytotrophoblasts may also play a role in the termination of early pregnancy.