Three product forms of methionine hydroxy analogue were prepared for biological evaluation of their l-methionine activity for broiler strain chickens (Vantress × Arbor Acres).Two samples of the acid of the analogue HA-50, LMA-70 and one sample of a commercial grade (90%) MHA® were standarized by gas liquid chromatography to contain a known amount of l-methionine activity as the free analogue acid.Each product form was tested in a separate experiment. The experimental chickens were fed a practical corn-soybean meal basal diet for the first seven days of the test. A semi-purified diet composed primarily of cerelose, isolated soybean protein and soybean meal was used for the remainder of the experimental period.HA-50 and the commercial form of the hydroxy analogue were formulated to contain 50% l-methionine activity. Hence, they were added to the diets at 0.1 and 0.2% and compared to the l-methionine standard which was added at levels of 0.05, 0.1 and 0.15%. LMA-70 was formulated to contain 70% l-methionine activity and was added to the experimental diets at 0.07 and 0.14% and compared to the l-methionine standard at the same levels used in the other experiments.Statistical analysis of four-week data revealed no difference between the biological response of l-methionine and the three forms of the analogue when tested at comparable l-methionine activity levels. The biological response of the analogue products was in good agreement with the l-methionine activity determined by gas liquid chromatography.