No effect was shown of 3-amino-l,2,4-triazole (amitrole) upon the incorporation of alanine or histidine into soluble protein in bean (Phaseolus vulgaris L.) hypocotyls grown in darkness. The metabolic derivative of amitrole, β-(3-amino-1,2,4-triazolyl-l-)α-ala-nine (hereinafter referred to as 3-ATAL), also had no effect upon histidine incorporation. Serine incorporation was increased 56% in the presence of amitrole, but this may result from a reduction of endogenous serine pools. No evidence indicates a general disruption of protein synthesis. Activity from amitrole-5-14C was readily incorporated into bean protein, but hydrolysis revealed no 3-ATAL. Most of the activity was recovered as amitrole. Amitrole in the presence of riboflavin and light attacked bovine serum albumin, probably by free radical formation. Hydrolysis of bovine serum albumin revealed mainly amitrole. Apparently, the entry of amitrole into bean protein is by free radical formation.