Two experiments were conducted to determine the vitamin B-6 requirement for growing kittens. Ten kittens were divided into two groups and given a purified diet containing 8.0 mg pyridoxine (PN)/kg diet (+PN) or a PN-free diet (-PN) for 11 wk. Daily body weight gain, food intake, weekly plasma free amino acids, plasma B-6 vitamers, urinary oxalate excretion, hemoglobin (Hb) and hematocrit were measured. Kittens fed a -PN diet had depressed body weight gain, food intake, plasma pyridoxal phosphate (PLP) and pyridoxal (PL), Hb and hematocrit, and had elevated urinary oxalate, plasma tyrosine and plasma cystathionine. In a second experiment, 24 kittens were given a -PN diet for 45 d to deplete their body reserves. The kittens were then divided into six groups of four kittens each and given a purified diet containing either 0.5, 1.0, 2.0, 3.0, 4.0 or 8.0 mg PN/kg diet for 46 d. Following supplementation, positive responses in body weight gain, PLP, Hb and hematocrit, and decreased urinary oxalate excretion, plasma tyrosine and plasma cystathionine occurred in all groups except those fed 0.5 mg PN/kg diet. At the end of the repletion period, kittens fed 1.0 mg PN/kg diet had lower body weight gain, higher plasma tyrosine and cystathionine, slower rate of decrease in urinary oxalate, and lower values for Hb, hematocrit and PLP than did the kittens from groups fed 2.0-8.0 mg PN/kg diet. These findings indicate that the dietary requirement for PN is greater than 1.0 mg/kg diet, but 2.0 mg PN/kg diet is adequate for growing kittens given a 35% casein diet.