Methionine and its derivatives are used as feed supplements. The objective of this study was to compare the effectiveness of DL-methionine (MET), DL-methionine-hydroxy-analogue (2-hydroxy-4-methylthio-butyric acid, MHA), and DL-S methyl-methionine-sulphonium-chloride (SMM) in rats using low- (10 g/100g, BD10), medium-(15g/100g, BD15) and high-protein (20 g/100 g, BD20) diets. In a 10-day growth assay with weaning male rats (Wistar, SPF, LATI, Gödöllo, Hungary, 6 rats/group) methionine-deficient basic diets (BD10, BD15, BD20) were supplemented with 0, 1.5 ad 3.0 g/kg MET, MHA OR SMM. Extracted soybean meal was used as sole protein source. A protein-free diet was used for determining net protein ratio (NPR) indices. The weight gain of rats fed test diets fortified with 1.5 and 3.0 g/kg MET, MHA, or SMM was significantly higher (p < 0.05) than that obtained with the unfortified diets. The NPR index of the diets was increased by MET, MHA or SMM supplementation, which increase was significant (p < 0.05) at 3.0 g/kg fortification level. However, there were no significant differences between the efficiencies of methionine derivatives on the same dietary protein levels. The weight gains of the rats were higher and the NPR indices of the diets were lower at a higher dietary protein level.