Biochemical and morphological modifications occurring in the pancreas of multiple low dose streptozocin treated rats, subjected to a preventive or concomitant immunosuppressive administration of Cyclosporin A (CyA 8mg/Kg b. wt./45 days), were observed. Biochemical assays showed that CyA significantly enhances glycaemia (p less than 0.0001) and decreases serum insulin levels (p less than 0.0001), while serum creatinine was slightly increased (p less than 0.05). Morphological findings (L.M. and T.E.M.) of rats, diabetized during the CyA administration, demonstrated a variable degree of survival of B- cells (damaged and undamaged cells were noted) and areas of modified exocrine cells (extended vacuolation). Pancreases of rats, first immunosuppressed then diabetized, showed similar ultrastructural features to those of the previous group but presented a greater B-cell loss. It is evident that CyA is only moderately effective against direct cytotoxic effects of STZ, when given concomitantly, and completely fails to protect B cells when given prior to the diabetogenic drug.