The excretion of noscapine in human breast milk was studied in 8 lactating women given a single oral dose of 100 or 150 mg after a light breakfast. Serum and milk samples were collected for 24 h after drug intake. Although noscapine is a weak base, only a small amount was excreted in the milk. The median milk/serum ratio was 0.29, range 0.15-0.88. The noscapine dose received by a child during a 24 hour period, when the maternal dose is 50 mg t.i.d., was calculated to be 0.8 (0.4-1.9) micrograms/kg (median and range).