Rats turned diabetic by alloxan treatment are refractory to systemic anaphylactic shock, in a direct association with reduced intestinal haemorrhage and tissue response to antigen challenge. As diabetic rats show reduction in mast cell numbers in different body compartments, this study was undertaken to investigate the influence of alloxan diabetes on mast cell population as well as the expression of the mast cell growth factor interleukin (IL)-3 in the small intestine of rats. We also analysed the putative involvement of endogenous insulin and glucocorticoid hormones in this phenomenon. There was a significant decrease in the number of mast cells present in the small intestine (ileum segment) of diabetic rats. Likewise, the immunohistochemical analysis revealed that IL-3 labelling was markedly attenuated in diabetic rats, as compared with normal animals, a phenomenon which paralleled with a decreased mRNA expression as attested by Reverse transcriptase-polymerase chain reaction technique. Treatment with insulin and with the steroid receptor antagonist RU 486 restored basal mast cell numbers, normal levels of IL-3 labelling and mRNA expression for IL-3 in the ileum of diabetic rats. In conclusion, our findings show that there is a causative relationship between down-regulation of mast cell numbers and the expression of IL-3 associated with diabetic state. In addition, as both parameters were suppressed by administration of insulin and RU 486, it indicates that an imbalance between the systemic levels of insulin and glucocorticoid hormones seems to be implicated in the reduction in intestinal mast cell population and refractoriness to antigen provocation in alloxan diabetes.