OBJECTIVE: To compare the antifertility effects of 50% ethanolic extract of the root bark of Cananga odorata with gossypol. DESIGN: Controlled research laboratory study. SETTING: University research laboratory. ANIMAL(S): Male albino rats (Sprague Dawley, body weight 150 +/- 5 g) bred in university animal house. INTERVENTION(S): A 50% ethanolic extract of the root bark of Cananga odorata and gossypol was administered orally for 60 days. On day 61, one third of the animals in each group were killed for various analyses. One half of the remaining animals were used for the evaluation of fertility index, and other half was maintained for 15 days more on normal diet. MAIN OUTCOME MEASURE(S): The epididymal sperm motility, morphology, and count, the testicular activities of HMG CoA reductase, 3beta-hydroxy steroid dehydrogenase, glucose-6-phosphate dehydrogenase, and testicular cholesterol and serum testosterone were assessed. RESULT(S): Differences were not observed in the sperm count and fertility index of the gossypol group in comparison with the C odorata group. But statistically significant alterations were noted in the sperm morphology as well as in the activity of HMG CoA reductase, 3beta-hydroxy steroid dehydrogenase, glucose-6-phosphate dehydrogenase, cholesterol, and protein of the testis and in serum testosterone. On withdrawal of the drugs, sperms in C odorata group became completely motile but not in the gossypol group. The active component is a 52 kd protein. CONCLUSION(S): The ethanolic extract of Cananga odorata possesses antifertility effects.