The VLDL and LDL fractions were isolated from 29 patients with type 1 diabetes at the time of admission to the hospital to restore glycemic control and again at discharge. These lipoprotein fractions were incubated with human monocyte-derived macrophages, and the rates of macrophage CE synthesis were determined. The rates of CE synthesis in human macrophages were significantly greater (P less than 0.005) when incubated with VLDL isolated from type I diabetic patients before compared with after glycemic control was attained and averaged 1.84 +/- 0.52 and 1.09 +/- 0.27 nmol (1.20 +/- 0.34 and 0.71 +/- 0.18 micrograms) [14C]cholesteryl oleate synthesized.mg cell protein-1 x 20 h-1, respectively. In contrast, when LDL isolated from the same patient during the same period was incubated with human macrophages, the rates of cellular cholesteryl ester synthesis did not differ significantly and averaged 4.23 +/- 1.26 and 3.91 +/- 0.96 nmol (2.75 +/- 0.82 and 2.55 +/- 0.63 micrograms) [14C]cholesteryl oleate synthesized.mg-1 cell protein.20 h-1, respectively. There was a significant increase in the total cholesterol content of VLDL isolated before glycemic control compared with that isolated after glycemic control was attained (P less than 0.05) resulting from a significant increase in the FC and CE (P less than 0.05) contents of these VLDL particles. There was a significant decrease in the ratio of FC to PL in VLDL, but not LDL, isolated after glycemic control (P less than 0.05). The percentage of apoE in VLDL was significantly decreased (P less than 0.05) after glycemic control was attained.(ABSTRACT TRUNCATED AT 250 WORDS)