In carefully dissected neck veins, no evidence was found of platelet adherence to the vessel wall or leucocyte migration. However, 30-60 min of total stasis led to polymorphonuclear leucocytes sticking to the endothelium and their subsequent migration. This migration across the vessel wall resulted from stasis and not the trauma of dissection. Adherence and migration of leucocytes did not cause gross endothelial cell damage or desquamation within the observed period of stasis and there was no associated platelet adherence following restoration of blood flow. Thus leucocyte migration does not impair the non-thrombogenicity of the endothelium in acute experiments.