A series of five randomised-block experiments, involving 232 finishing beef steers., have been carried out to examine the effects of supplementing grass silage-based diets with extracted soyabean meal (SBM) or fish meal (FM). Eight formic-acid treated, precision chopped, silages which were made from the primary growth and first and second regrowths of perennial ryegrass swards, were used. The chemical compositions of the silages are given in Table 1. They were offered ad libitum and those used in experiments 1 to 3 and the early-cut silages used in experiments 4 and 5 were supplemented with 2.5 to 2.7 kg concentrates per head daily while the late-cut silages used in experiments 4 and 5 were supplemented with 4.5 kg concentrates per head daily. The control concentrates used in each of the experiments were based on barley and had crude protein concentrations of 95 to 108 g/kg dry matter. The high protein concentrates were similar but with a proportion of the barley replaced by SBM or FM.