The major 3β-hydroxy-Δ5 steroids in the monosulphate and disulphate fractions of faeces from infants 2 weeks to 6 months of age have been assayed by gas chromatography-mass spectrometry. The steroid concentration was highest in a pool of faeces collected from infants 6 to 8 weeks of age, viz: 3β,16α-dihydroxy-5-androsten-17-one, 300 μg/100 g; 3β,16β-dihydroxy-5-androsten-17-one, 360 μg/100 g; 5-androstene-3β,16α,17β-triol, 570 μg/100 g; 3β-hydroxy-5-pregnen-20-one, 810 μg/100 g; 3β-hydroxy-5,16-pregnadien-20-one, 240 μg/100 g; 3β,16α-dihydroxy-5-pregnen-20-one, 1670 μg/100 g; 5-pregnene-3β,20α-diol, 700 μg/100 g and 5-pregnene-3β,16α,20α-triol, 220 μg/100 g. The quantitative relationships between the steroids changed with increasing age of the infants. In the samples collected from infants older than three months of age, 5-pregnene-3β,20α-diol replaced 3β,16α-dihydroxy-5-pregnen-20-one as the principal steroid metabolically related to 3β-hydroxy-5-pregnen-20-one. A comparison between the daily excretion of 3β,16α-dihydroxy-5-pregnen-20-one in the faeces and the published values for the urinary excretion of this steroid, suggests that during early infancy as much steroid is excreted in the faeces as in the urine.