The p.d. of the rat seminiferous tubules was 4.75 +/- 1.39 mV (lumen negative) at 35 degrees C and varied linearly with temperatures from 26 to 40 degrees C. A depolarization of the seminiferous tubules was found in the rats administered with gossypol at the dosage of 30 mg/kg body weight for 3 weeks, the p.d. lowered to 3.63 +/- 0.79 mV at 35 degrees C and was independent of the changes of seminiferous tubules temperature. In the 5-week-gossypol-treatment group, the tracer penetrated not only the myoid cell layer, but also went beyond the tight junction complexes between Sertoli cells. The lanthanum appeared in the cleft surrounding spermatogonia. In the 8-week-gossypol-treatment group, the lanthanum was found in the adluminal compartment. It indicates that gossypol can cause a dysfunction of the Sertoli cells and blood-testis barrier and disturb a good physiological environment for the developing spermatocytes.