The purpose of this study was to characterize the lipoprotein profile in the KKA7mouse, a rodent model of type II diabetes, before and after treatment with the insulin-sensitizing drug pioglitazone. Analysis of the plasma from untreated KKA7mice showed that they were severely hyperglycemic, severely hypertriglyceridemic, and moderately hypercholesterolemic. Agarose column chromatographic analysis showed that essentially all of the triglyceride eluted with very low density lipoprotein, and the majority of the cholesterol eluted with high density lipoprotein. Thus, both the very low density lipoprotein and high density lipoprotein levels were markedly elevated in KKA7mice. Analysis of the lipoproteins by agarose electrophoresis-immunoblotting showed that apoprotein A-I and apoprotein B had aberrant electrophoretic behavior, typical of apoproteins that have been modified by nonenzymatic glycosylation. Treatment of KKA7mice with pioglitazone for 8 days caused a marked reduction in blood glucose and plasma triglyceride concentrations but had no significant effect on plasma cholesterol concentration or distribution. The aberrant electrophoretic behavior of the apoproteins was corrected to normal by drug treatment These data show that the KKA7mouse has a severe dyslipoproteinemia that is probably secondary to its insulin resistance, but that its lipoprotein profile differs significantly from that of the insulin-resistant human in that the majority of the plasma cholesterol is carried in high density lipoprotein, and those high density lipoprotein levels are very high.