The effects of glipizide on HDL subclass levels were prospectively evaluated in 7 women and 2 men with non-insulin dependent (Type 2) diabetes. Total HDL, HDL2 and HDL3 levels were unchanged during the treatment period. Baseline HDL levels were lower when compared to a control population which may have been due to the elevated body weight present in most subjects. Mean blood glucose and HbA1 levels were unchanged for the entire group although significant improvement was noted in 5 individuals. Triglyceride and cholesterol levels were not affected by treatment with glipizide. In conclusion, glipizide does not have an adverse affect on HDL lipoprotein levels when patients are followed prospectively.