Ivermectin levels were measured in breastmilk and plasma of 4 healthy mothers after an oral 150 micrograms/kg dose. Mean +/- S.D. plasma and milk values were 37.9 +/- 0.54 and 14.13 +/- 0.43 (ng/ml) respectively. Steady-state ivermectin levels in milk were low. Our results suggest that exclusion of lactating mothers from mass chemotherapy with ivermectin may be unnecessary.