The present experiment was undertaken to study what types of human cancers are responsive to the antiproliferative effects of suramin. The human malignant cells used were as follows: cervical cancer (HeLa), mammary cancer (MCF-7), bladder cancer (EJ), hepatoma (HuH-7, PLC/PRF/5), embryonal carcinoma (PA-1), in vitro transformed fibroblasts (KMST-6, SUSM-1, VA-13), five myeloma cell lines (KMM-1, KMS-5, KMS-11, KMS-12, RPMI 8226), Burkitt's lymphoma (Raji), acute promyelocytic leukemia (HL-60), chronic myelocytic leukemia (K562), Epstein-Barr virus nuclear antigen positive lymphoblastoid cells (KMS-9). The cells were treated with 25 to 100 micrograms/ml suramin for 72h. Proliferation of HuH-7 and two human myeloma cells (KMS-11 and KMS-12) was remarkably inhibited, and that of PA-1, PLC/PRF/5, KMST-6, two other myeloma cell lines (KMM-1 and KMS-5), Raji and HL-60, was moderately inhibited. In order to confirm part of the results obtained from in vitro experiments, in vivo experiments were also undertaken. The growth of HuH-7 cells transplanted subcutaneously into nude mice was significantly suppressed by intravenous injection of suramin. We discussed the possibility that certain types of human cancers, the growth of which seemed to be more or less dependent on polypeptide growth factors, might be sensitive to the antiproliferative effects of suramin.