Angiogenic immature capillaries in human granulation tissue possess many cytoplasmic interdigitations between endothelial cells and pericytes (CIDEP). Epidermal growth factor (EGF) is a potent mitogenic polypeptide which accelerates angiogenesis in vivo and in vitro. We have recently demonstrated in immature capillaries that EGF is present at the CIDEP and proposed that the CIDEP may be involved in a signaling pathway for EGF (Wakui et al., 1990c. Microvasc. Res. 40, 285-291). This study follows that previous report. In the present study, I have investigated the ultrastructural localization of the EGF receptor (EGF-r) at CIDEP. Immunoreactivity for the EGF-r in immature capillaries was located strictly at the CIDEP in large numbers, at the coated pits and vesicles of endothelial cells, and at some lysosome-like structures of the endothelial cells and the pericytes. On the other hand, immunoreactivity for EGF-r was absent in mature capillaries. At the CIDEP, EGF-r immunoreactivity was present at the cell membrane and a few cytoplasmic elements at the tip of pericyte cytoplasmic projections, but it was completely absent at the corresponding endothelial membrane indentation. The present results support our proposed hypothesis that the CIDEP in immature capillaries act as a pathway for EGF transportation from the endothelial cell to the pericyte by a receptor-mediated process.