1. Cholesterol intake (about 0·25 mmol/day) and the faecal excretion of cholesterol, coprostanol and coprostanone were determined in normolipidaemic control subjects and hyperlipidaemic patients, whose bile acid kinetics had been previously studied.
2. The combined excretion of the neutral steroids (excluding plant sterol and plant sterol metabolites) averaged 1·07 ± 0·13 (± sem) mmol/day in the control subjects (n = 14). The corresponding values in patients with hyperlipoproteinaemia type IIa (n = 19), II (n = 12) and IV (n = 23) were 0·86 ± 0·10, 0·93 ± 0·11 and 1·48 ± 0·17 mmol/day respectively.
3. The mean values for the net steroid ‘balance’, defined as the combined amount of bile acid synthesized (determined by an isotope-dilution technique) and the faecal excretion of neutral steroids minus cholesterol intake, were 1·83 ± 0·22 mmol/day in the control subjects and 1·60 ± 0·15, 1·81 ± 0·19 and 3·53 ± 0·23 mmol/day in patients with type IIa, IIb and IV lipoprotein patterns respectively.
4. No significant correlations between net steroid ‘balance’ and sex, age, serum lipid concentrations, body weight or body surface area were found in any of the groups of subjects.
5. It is concluded that patients with type II hyperlipoproteinaemia eliminate cholesterol as bile acids and neutral faecal steroids normally. The type IV lipoprotein pattern is associated with increased bile acid synthesis and/or elevated faecal excretion of neutral steroids, so that the net steroid ‘balance’ is usually above the normal limit.