A series of experiments was conducted using White Leghorn male chicks to study the arginine-lysine relationship in rapeseed meal (RSM). Semi-purified diets containing 15% protein either from RSM or soybean meal (SBM) were fed. Arginine supplementation completely reversed the growth depression caused by the addition of lysine to RSM diets. Potassium acetate was only partially effective in alleviating the growth depression caused by supplemental lysine, while polyvinyl pyrrolidone significantly reduced chick performance. Tannic acid addition (1.5%) to SBM diets resulted in a severe growth depression which was partially corrected by the supplementation of arginine in the presence of methionine. Supplementation of these amino acids to RSM had a less drastic effect. It is suggested that a portion of the arginine in rapeseed meal may be required for metabolic processes involved in tannic acid excretion.