The production of Interleukin 1 (Il1) by circulating blood monocytes and alveolar macrophages was studied in melanoma patients. There were 144 patients in the monocytes study and 5 patients in the alveolar macrophages study. The Il1 activity was tested by a bioassay and reported in units based on the integration of the area under the curve. This was shown to be preferable to the standard method, i.e. probit analysis. Results showed that there was no depression of Il1 activity in melanoma patients as compared to control (98 + 32 units, versus 100 units). There was no difference when the values were compared according to sex, age and stage of the disease. However, a significant difference was found between phototype I and phototype IV. Alveolar macrophages, in all experiments (n = 5), had a significantly lower Il1 activity than the autologous monocytes. It is concluded that we can question the relevance of Il1 production by peripheral blood monocytes to the state of the immunity of melanoma patients.