Adult endometrium is a tissue in which physiological angiogenesis occurs regularly and provides an accessible source of material for study. Endometrial biopsies and immunohistochemistry were used to test two hypotheses: firstly, that there are peaks of endothelial cell proliferation in human endometrium during the menstrual cycle, and secondly that in-vitro endothelial cell migratory signal production by human endometrium (measured in a previous study) accompanies endothelial cell proliferative activity in vivo. Proliferating cells were identified using anti-proliferating cell nuclear antigen, and endothelial cells were identified using anti-CD34. The method was validated by a smaller, separate study using bromodeoxyuridine incorporation and detection with formalin-fixed biopsies, and comparison with proliferating cell nuclear antigen staining. The main study (n = 50) showed that significant peaks of endometrial endothelial cell proliferation could not be identified, due to the large variability in endothelial cell proliferative activity between individuals at the same stage of the menstrual cycle. Endometrial endothelial cell migratory signal production did not correlate with endothelial cell proliferation (n = 27). Results suggest that blood vessel growth in the endometrium may occur by a process that differs from the traditional concept of angiogenesis, which has been derived mainly from in-vitro or in-vivo experimental studies.