A parallel-plate perfusion chamber has been used to evaluate the contribution of the adhesive membrane glycoprotein CD36 (GPIV) to platelet adhesion on type I collagen in flowing whole blood at a shear rate of 800 s-1. In one series of experiments, reconstituted normal blood (hematocrit 0.4; platelet count 1.5 x 10(5)/microL) was prepared from washed red blood cells, plasma, and washed platelets that had been incubated with Fab fragments of a monospecific polyclonal anti-CD36 antibody (50 micrograms/mL, 30 minutes, 37 degrees C). Percent surface coverage of collagen-coated coverslips using reconstituted blood with antibody-blocked platelets, as compared with paired reconstituted controls (100%), was 50% at 2 minutes, 87% at 5 minutes, and 90% at 10 minutes. Further studies were performed by perfusion of whole blood from a healthy donor of the Naka-negative phenotype, whose platelets constitutively lack CD36, over collagen-coated coverslips. In this case, percent surface coverage was 55% of normal controls at 2 minutes, 76% of controls at 5 minutes, and 72% of controls at 10 minutes. In both preparations, platelets lacking functional CD36 had a statistically significant decrease (P < .005) in adhesion after 2 minutes and 10 minutes perfusion but not at 5 minutes. These results show that functional CD36 facilitates the rapid adhesion of platelets to collagen and that this effect is seen at the earliest time points of their interaction.