Two trials, one with 36 twin-suckling Chios ewes and the other with 32 twin-suckling Damascus goats, were conducted to study the effect of protein source (fish meal v. soya-bean meal) on the pre-weaning milk yield of the dams, and the growth performance of their offspring. The control (C) concentrate mixture was similar in both trials, using soya-bean meal (SBM) (195 kg/t) as a source of supplemental protein. In the experimental diet (FME) of the ewe trial, SBM was replaced completely by fish meal (FM) whereas in the goat trial (FMG) 83 kg of SBM were replaced by 50 kg FM. Dry matter (DM) and crude protein (CP) degradation of the three isonitrogenous mixtures were measured using nylon bags incubated in the rumens (2, 6, 16, 24 and 32 h) of three Damascus goats. There were no significant differences between mixtures for DM and CP effective degradability at 005 per h outflow rate. At 0·08 per h outflow rate however, lower degradability values were obtained with the FME than with the C diet. There were differences in the effective CP degradability of SBM and FM used in the ewe trial, but the FM used in the goat trial was of higher CP degradability and similar to that of SBM. Ewes on FM produced more milk than those on the control diet (C 3·44 v. FME 3·84 kg/day), whereas milk yield of goats was similar in the two treatments (C 3·87 v. FMG 3·82 kg/day). There were no differences between treatments for ewe milk fat (C 44 v. FME 43 g/kg) or protein concentration (C 54 v. FME 53 g/kg). Goats on fish meal (FMG) produced milk of higher protein (C 37 v. FMG 40 g/kg), but of similar fat (C 42 v. FMG 43 g/kg) concentration to those on the SBM (C) diet. With the exception of the better conversion (milk: gain ratio) efficiency (C 5·17 v. FME 4·44) of male lambs sucking ewes on the FM diet, no other differences were observed in the performance of lambs or kids. Lambs consumed less milk than kids (lambs: males 4·69, females 5·13; kids: males 6·63, females 6·98) per unit of weight gain.