Chick growth assays were used to evaluate the efficacy of poly-L-methionine and DL/LD methionylmethionine ( a 50:50 mixture of D-Met-L-Met and L-Met-D-Met). The polypeptide possessed no bioefficacy whatever, probably due to its extreme insolubility. The dipeptide of methionine exhibited growth-promoting ability equal to that of DL-methionine itself.