The effect of different amounts and types of dietary fat on faecal steroid excretion in healthy volunteers was examined. In the first experiment with sixty volunteers four diets which differed in type and amount of dietary fat only were compared during a test-period of 5 weeks. Faeces were collected during 7 days before and at the end of the test period and analysed individually. In the second experiment with thirty-five volunteers, a low fat diet containing 22% of energy as total fat (4% as polyunsaturated fatty acids) was compared with a moderate fat diet (30% of energy as total fat; 11% as polyunsaturated fatty acids) during 13 weeks. Faeces were collected during the first 7 days of the test period and during 7 consecutive days near the end of the test period and pooled per dietary group. Excretion of faecal neutral steroids and bile acids was not significantly influenced by amounts of total fat ranging from 22% to 40% of daily energy or by differences in polyunsaturated to saturated fatty acids ratio from 0 . 2 to 1 . 7. The only exception was the excretion of bile acids in the second experiment which was 0 . 19 mmol/24 h (75 mg/24 h) higher on the low fat diet than on the moderate fat, high polyunsaturated fat diet (P less than 0 . 01).