Although most of the initial studies in angiogenesis were done on solid tumors, there is now data suggesting the importance of angiogenesis in hematologic malignancies. We estimated bone marrow microvessel density before autologous stem cell transplantation and at the time of response in 13 patients with myeloma (seven complete and six partial responders) using an immunohistochemical stain for factor VIII-related antigen (von Willebrand factor). Baseline microvessel density was significantly different between bone marrow samples from patients with myeloma and morphologically normal, staging marrows from patients with limited stage Hodgkin's disease, mean (+/- s.d.) 294 (+/-115)/mm2 vs 93 (+/-26/mm2, respectively, P = 0.001. After transplantation, microvessel density continued to be high in myeloma samples compared to samples from control patients with limited stage Hodgkin's disease, mean (+/- s.d.) 230 (+/-68)/mm2, P = 0.003. There was no difference in microvessel density at the time of complete or partial response compared to values prior to transplantation. This report confirms that increased angiogenesis is found in myeloma bone marrow prior to transplantation, and suggests that increased angiogenesis persists even after complete response.