Abstract Diurnal variation in plasma-cortisol was studied immediately before and after intermittent steroid therapy in seven patients receiving monthly courses of quadruple chemotherapy for Hodgkin's or non-Hodgkin's lymphoma over a period of 6 months. The serum-thyroid-stimulating-hormone (T.S.H.) response to intravenous T.S.H.-releasing factor was also measured before and during the first course and before the second and fourth courses. The morning plasma-cortisol concentration fell significantly over 6 months when measured immediately before the start of each course. The mean evening cortisol concentration also fell over this period. In most patients the T.S.H. response showed a downward trend during treatment, although in two patients the response returned to normal whilst they were still undergoing therapy.