1. The relative potencies of three lysine, one tryptophan and six methionine analogues to their corresponding l-amino acids were determined. 2. Male poults, 9 d of age, were used in five 14 d experiments. Experimental diets were formed by adding increasing levels of an amino acid (L-isomer) or its analogues to a basal diet deficient in the test amino acid. Multiple-regression analyses of body-weight gain v. level of added or amount of consumed amino acid supplement were computed. Relative potencies of the analogues were calculated using the slope-ratio technique. 3. Type of independent variable used in the regression analyses did not significantly affect relative potency values. 4. From regression analyses with level of added amino acid supplement as the independent variable, relative potencies (with 95% confidence intervals) on a molar basis of each analogue as a percentage of the respective amino acid were: hydroxymethyl-L-tryptophan monohydrate 9(-12, 22), DL-methionine sulphone 3 (-68, 36), DL-methionine hydantoin - 10 (-63, 29), L-cystine 8 (-31, 40), DL-methionine sulphoxide 59 (24, 95) and 46 (18, 74), oleoyl-DL-methionine 77 (37,138), methionine hydroxy analogue calcium 93 (65, 128), dicocoyl-L-lysine 23 (5,41), bis-hydroxymethyl-L-lysine-calcium 69 (54, 84 and 41 (-1,80), mono-hydroxymethyl-L-lysine-calcium 89 (77, 101) and 99 (65, 134). 5. The first four analogues appeared to have little or no amino acid activity. DL-methionine sulphoxide, dicocoyl-L-lysine, and bis-hydroxymethyl-L-lysine -calcium were partially active. Relative potencies of oleoyl-DL-methionine, methionine hydroxy analogue calcium, and mono-hydroxymethyl-L-lysine- calcium were not significantly different from those of their corresponding amino acids.