Nine patients with Kaposi's sarcoma and five suffering from T-cell lymphoma have been examined. Antibodies to HTLV-1 were not found in these patients. The primary cellular cultures were isolated from blood and lymph nodes of the patients. Viral particles (type C) were found in the culture obtained from the patient with lymphoma of T-cell origin. DNAs from the primary cellular cultures from patients with lymphoma or sarcoma contained the sequences homologous to gag-gene of HTLV-1. The data suppose the patients with T-cell lymphoma and Kaposi's sarcoma to carry HTLV-1 virus.