Eight Limousin-cross steers (355 kg) were used in a replicated 4 x 4 Latin-square designed to estimate lysine requirements. Steers were fed a semipurified diet containing little ruminal escape protein. Treatments were abomasal infusions of 0, 8, 16, or 24 g/day L-lysine. All steers were additionally infused with 400 g/day dextrose and 285.9 g/day of an amino acid mix that contained (g/day) L-methionine (12.0), L-histidine (8.1), L-arginine (10.5), L-threonine (12.0), L-valine (18.0), L-isoleucine (13.8), L-leucine (27.3), L-phenylalanine (28.2), L-glutamic acid (76.5), glycine (76.5) and L-tryptophan (3.0); it had been demonstrated previously that when lysine was included in this infusion mixture, nutritional requirements of steers for maximal N retention were met or exceeded. Nitrogen retention averaged 38 g/day and was not affected by treatment, implying that the lysine requirement of steers was less than the 37.8 g/day lysine estimated to be absorbed from the small intestine when the basal diet was fed.