Cytoplasmic interdigitations between the endothelial cells and pericytes (CIDEP) consist of a pericyte cytoplasmic projection and corresponding endothelial indentation. These are frequently present at the angiogenic sites. We have ultrastructurally examined CIDEP numbers at angiogenic sites induced by a polyvinyl alcohol foam disc implanted subcutaneously in rats. On Day 3 after implantation, the CIDEP number per endothelial cell and pericyte was similar to that of normal subcutaneous tissue, and then increased sharply with time to peak on Day 10. After this, it decreased, and on Day 30 was similar to that of normal subcutaneous tissue. The capillary density on Day 3 was significantly lower than that of normal subcutaneous tissue, increasing to peak on Day 7, and then decreasing with time. Until Day 7, capillary size was significantly smaller than in normal subcutaneous tissue, then increased with time. On Day 10, the number of endothelial cells significantly decreased, and that of pericytes significantly increased. The present study indicated that the predominant CIDEP distribution was observed on Day 10 following the active vascular proliferation stage on Day 7 and was concomitant with a decline in the number of the endothelial cells and an increase in the number of the pericytes.