A comparative study of two antiemetic neuroleptics, metoclopramide and metopimazine, effects on the oestrus cycle of female rats has been done. These compounds were administered once daily for 21 consecutive days (1, 0,1, 0,01, 0,001 mg/kg/s.c.) on Wistar AFSPF rats, exhibiting regular four day cycles. Evolution of oestrus cycle was studied by daily vaginal smears. Our data show that metoclopramide does not influence oestrus cycle, while metopimazine suppress oestrus cycles, substituted for a permanent dioestrus. For the last compound, a statistically significant difference between treated and controls is demonstrated.