Although cyclosporine A (Cy-A) is effective in modifying the initial course of newly diagnosed insulin dependent diabetes mellitus (IDDM) it has a number of side effects, particularly renal, which limit its use. In this study we investigated the potential synergistic effects of bromocriptine (BCR) therapy in treating patients with newly diagnosed IDDM. Three groups of patients were treated: (1) fourteen patients on Cy-A who required a decrease in their dose due to elevated creatinine; (2) four newly diagnosed patients whose initial therapy consisted of low dose (5 mg/kg/day) Cy-A and 10 mg/day of BCR; (3) eight patients whose glucagon-stimulated connecting-peptide (C-peptide) levels were greater than 0.3 nmol/l but whose insulin requirements were over 0.3 U/kg/day and whose Cy-A was to be discontinued. The results suggest that there was no statistically significant difference in stimulated C-peptide, glycosylated haemoglobin, daily insulin dose or serum creatinine. However, the trend suggested that BCR may have some protective effect on preserving endogenous insulin secretory capacity, although glycosylated haemoglobin and daily insulin dose increased. The results do not suggest that patients with newly diagnosed IDDM significantly benefit from concurrent BCR and Cy-A therapy.