Objective: To investigate the allergic reaction in neonatal streptozotocin (nSTZ)-induced diabetes mellitus. Material: Male newborn Wistar rats were made diabetic by the injection of streptozotocin (160mg/kg, i. p.) and used 8 weeks thereafter. Treatment: Animals were sensitized against ovalbumin (OA, 50µg and Al(OH)3, 5mg, s. c.) and challenged 14 or 21 days thereafter. Methods: OA-induced airway inflammation and OA-induced pleurisy models were used to investigate leukocyte migration (total and differential leukocyte counts) and lung vascular permeability (Evans blue dye extravasation). Results: nSTZ-diabetic rats presented glucose intolerance and insulin resistance. Relative to controls, nSTZ rats exhibited a 30% to 50% reduction in lung vascular permeability. Leukocyte infiltration in both models of allergen-induced inflammation, and number of pleural mast cells did not differ between groups. Conclusions: Data suggest that the reduction of allergic inflammatory reactions in nSTZ rats is restricted to microvascular dysfunctions and associated, probably, with insulin resistance in lung microvascular endothelium.