Growth rate, egg number, egg and adult body weight, plumage condition, food intake and efficiency of laying hens were compared in birds differing in plumage colour genotype at five loci (C, I, S, Ig, B). 2. Laying rates of the different genotypes were not different. 3. Growth rate and adult body weight of females were significantly less in loci C and I white females as compared with the corresponding coloured females; there was a similar tendency in adult weight for the other loci, and in egg weight. Differences in body weight were more marked in birds kept in cages than in those kept on the floor. 4. For all loci the genotype suppressing colour was associated with less plumage deterioration, this being highly significant for loci C and S. 5. Food intake, adjusted for body weight and egg production, was less in locus I white hens, in agreement with previous data concerning the C locus. 6. Pleiotropic effects associated with colour were suggested and their consequences on efficiency of egg production are discussed.
