Cancer cells of nonhematologic origin are rarely seen on routinely prepared peripheral blood smears. This report describes two patients with disseminated carcinoma, in near terminal state, one with malignant melanoma and another with transitional cell carcinoma of the ureteropelvic junction who developed carcinocythemia (CCA). A review of the English literature revealed only eight other cases in which CCA was documented. Four patients had a small cell bronchogenic ("oat cell") carcinoma, two had disseminated breast carcinoma and one each had advanced adenocarcinoma of ileum and abdominal rhabdomyosarcoma. The circulating malignant cells usually accounted for less than 10% of the nucleated blood cells, but in one patient comprised up to 80% of the leukocyte count. The mean time between detection of CCA and death was 5 weeks (median, 2 weeks) reflecting the fact that CCA is generally a terminal event.