Two experiments were designed to test the possibility of partially replacing fish-meal protein in rainbow trout either with maize-gluten meal (MGM) (experiment 1) or potato protein concentrate (PPC) (experiment 2). Rainbow trout (Oncorhynchus mykiss) 30 g initial average weight were given diets containing different levels of MGM or PPC proteins ranging from 0 to 0·4 or to 0·6 of dietary protein, respectively. Substitutions of fish meal either by MGM or PPC were carried out establishing two different total dietary protein levels; 350 and 450 g/kg. Results showed that the MGM diets were acceptable and gave a significant enhancement (over 0·37 in the better case) in nutrient utilization when compared with those including only fish meal. On the contrary, diets including PPC were poorly accepted, and the growth offish and nutrient utilization were negatively correlated with dietary levels of PPC. It is concluded that levels of MGM representing around 400 g/kg diet can be used in foods for rainbow trout, whereas PPC appears not to be a suitable protein source for those fish.