Abstract The effect of DL methionine, methionine hydroxyanalogue (MHA) and sodium sulphate on the nutritive value of lupin-seed protein and leaf-protein concentrate (LPC) from lucerne for rats and chicks was evaluated. Methionine and MHA markedly improved the biological value of both lupin- and LPC-proteins, but the effect of sodium sulphate was not significant. The supplement of organic sulphur-compounds improved the performance of chicks fed on lupin-seed meal, but the effect of sodium sulphate was negligible. There was no significant response to any of the organic and inorganic sulphur compounds in chicks fed on LPC diets. These results suggest that some factor other than methionine defiency is limiting the nutritive value of LPC for these animals.