SummaryTwelve 6–8 months old male Barbados Blackbelly lambs were used in a 4 × 4 latin square experiment with three replicates to study the utilization of diets made from local by-products and containing 64, 93, 125 or 143 g crude protein/kgD. M.Both dry-matter (mean 750·1 g/day) and digestible-energy (mean 6·2 MJ DE/day) intakes, and their digestibility coefficients increased, though not significantly, with increasing dietary protein concentration. However, nitrogen digestibility, urinary-nitrogen output and nitrogen retention all increased significantly (P< 0·01) with increasing dietary protein concentration.Metabolic faecal nitrogen and endogenous urinary nitrogen derived from the intercept of significant regressions of nitrogen intake against urine and faecal nitrogen outputs were 5·07 g/kg dry matter eaten and 3·46 g/day (0·35 kg W0·75) respectively. The diets had a mean biological value of 73·6%. The digestible crude protein requirements for maintenance were (g/day) 29·0, 38·4 and 26·6 when estimated from nitrogen retention, factorially and from live-weight performance respectively.