The authors compared the arrest of lactation by terguride, lisuride and deprenone. Terguride was administered to 14 women 2 X 0.5 mg by the oral route or 4 X 0.2 mg by the oral route for 21 days, lisuride to 41 women 2 X 0.5 mg or 4 X 0.2 mg by the oral route for 21 days, deprenone to 8 women 4 X 0.5 mg per day by the oral route for 21 days. Thus treated women were compared with women where lactation was arrested by mestranol, 0.15 mg per day for 7 days (15 women) and with normally lactating puerperial women (12 women). As expected, all tested methods were effective. No serious side-effects were observed. In the overall evaluation of different procedures where we included the suppression of lactation, the drop of the prolactin level, the incidence of the rebound phenomenon and side-effects of treatment, terguride and lisuride proved more suitable than deprenone and mestranol. The results of terguride were slightly more favourable than those of lisuride.