The chemotactic microphage function in combating and eliminating microorganisms is one of the most important features of the cellular immune system. Using a modified Boyden method we studied in vitro the chemotactic activity of the granulocytes in 5 patients suffering from chronic muco-cutaneous candidosis (CMCC), 3 of the familial and 2 of the non-familial type. To obtain quantitative results comparable to those of a control group, we investigated the granulocytes of 55 clinically and immunologically healthy persons by the same way. So we found, in comparison with the results of the controls, a striking reduction of the chemotactic granulocyte activity in all CMCC patients. This impairment of chemotaxis is apparently due to an inborn defect of the microphages. It is pointed out, however, that a non-specific stimulation of the immune system might be a promising way in the treatment of patients affected by CMCC.