Recently, lipoprotein (a) [Lp(a)] has been identified as a major risk factor for coronary heart disease. No data are available on the effect of improved metabolic control on plasma Lp(a) concentrations in subjects with type II diabetes mellitus, a group at high risk for coronary heart disease. We examined the effects of improved metabolic control on plasma lipid and lipoproteins and Lp(a) concentrations in 12 subjects before and after 21 days of tight metabolic control. Glycosylated hemoglobin declined from 8.9% to 6.9% (P less than .002). Lp(a) increased slightly from 21.4 to 25.8 mg/dL (P = .119) with improved metabolic control. There were no significant differences in total, low-density, or high-density cholesterol values, although the decline in triglyceride concentrations was statistically significant. The distribution of apolipoprotein (a) [apo (a)] isoforms in subjects with type II diabetes mellitus was not unusual and the apo (a) isoform patterns did not change with improved metabolic control. Although the number of subjects was small, there was no decline in Lp(a) concentrations with improved control and thus the effect of glycemic control on Lp(a) concentrations may be much smaller in type II than in type I diabetes. These results suggest that diabetic subjects with elevated Lp(a) concentrations should have intensive management of conventional cardiovascular risk factors such as high-density lipoprotein cholesterol (HDLC), low-density lipoprotein cholesterol (LDLC), and blood pressure.