A study was conducted to determine the pattern of cortisol metabolism by lymphocytes obtained from four groups of subjects: 27 male and female patients suffering from various types of malignancy other than malignancy of lymphatic tissues; and 26 healthy male and female controls. Known concentrations of cells were incubated with 1,2-3H-cortisol and the products were isolated by thin-layer and paper chromatography. Three metabolites were found to be produced by lymphocytes from both normal and cancer-bearing patients: 20α-hydroxycortisol, 20β-hydroxycortisol, and tetrahydrocortisol. Cells from the female control group were found to be more active than those from the male controls, while cells from cancer-bearing patients were markedly more active than the normal cells, regardless of sex. It is suggested that this finding of increased metabolism of cortisol by lymphocytes from patients with different types of malignancy other than lymphoma may provide the basis for a new diagnostic aid.