The concentration of chloroquine (CQ), dapsone (DDS) and pyrimethamine (PYR) in plasma and milk were measured following the coadministration of a single dose of chloroquine and Maloprim to lactating women. The milk to plasma area under the concentration-time curve (AUC) ratio ranged from 1.96 to 4.26 for CQ, 0.22 to 0.45 for DDS and 0.46 to 0.66 for PYR. Assuming a daily milk ingestion of 1 l by the infant, the maximum percentage of the maternal dose for CQ, DDS and PYR in milk was 4.2%, 14.3% and 45.6%, respectively, over a 9 day period.