By using an LKB 2277 Thermal Activity Monitor, the thermogenesis curves of human promyelocytic leukemia HL-60 cells growth were determined. It was found that the heat production rate grew almost exponential during the first 10 h. When treated by two series of water-soluble metalloporphyrins, the growth metabolism of HL-60 cells can be suppressed. The extent of inhibitory effect as judged from the multiplication rate constant, k, varied with different porphyrins. From these data, it was found that these water-soluble metalloporphyrins can inhibit the growth metabolism of cancer cells even if there is no light.