To study the effect of high glucose on the production of type IV collagen and laminin P1 from the cultured human umbilical vein endothelial cells (HUVEC), we measured type N collagen and laminin P1 from HUVEC that were cultured under different conditions. The concentrations of type IV collagen in the cultured medium for high glucose (30 mM D-glucose) were significantly higher than those for low glucose (5.6 mM D-glucose), L-glucose (30 mM), or mannitol (30 mM). The increase of type IV collagen was dependent on the glucose concentration in the medium. The contents of type IV collagen in the cultured cells were also increased in high-glucose incubation compared with low glucose or L-glucose incubation. In contrast, the levels of laminin P1 in the medium cultured with high glucose were similar to those with low glucose or L-glucose. These results suggest that the increased production of type IV collagen may contribute to the thickening of basement membranes and may be linked to the development of diabetic nephropathy.