ABSTRACT Male Wistar rats with streptozotocin-induced diabetes received a control diet and a pyridoxine-deficient diet. The animals were divided at random into four groups: control rats (CR), control diabetic rats (CDR), diabetic rats receiving a pyridoxine-free diet (DRB6), and diabetic rats receiving saline solution and no insulin treatment (DRSS). The experiment lasted 45 days. During the first 15 days the animals were observed for the development of diabetes and during the remaining 30 days they received the respective diets. The absence of vitamin B(6) did not influence the glycemia levels at the end of the experiment or the weight evolution of the animals. The rats that did not receive pyridoxine (DRB6) only showed a reduction in GPT activity (17.79 U/mL) compared to the other groups. The DRB6 group presented a significantly lower (p <0.05) nitrogen balance during each period (2.38 +/- 0.44 g N/7 days) compared to the CDR group (3.28 +/- 0.56 g N/7 days). The DRSS group presented similar or significantly higher values (2.81 +/- 0.77 g N/7 days) compared to the CDR group. Pyridoxine-deficient diabetic rats treated with insulin suffered important changes in the utilization of dietary proteins, as observed by nitrogen balance and enzyme activity studies.