To evaluate the immunological state in chronic renal insufficiency, the Authors studied cellular and humoral immunity in 292 patients with chronic renal failure. They were divided into 3 groups: 1) 37 with creatinine clearance between 50 and 20 ml/min; 2) 57 with creatinine clearance between 20 and 8 ml/min; 3) 178 treated by hemodialysis. In vivo and in vitro tests, that is DNCB, PPD skin tests, spontaneous, active and EAC rosettes, surface membrane immunoglobulin test, complement (C3, C4) and serum immunoglobulins were taken as markers of the immune response. Cell-mediated immunity was found to be significantly impaired in patients with terminal renal insufficiency or on hemodialysis and also markedly reduced in patients with non-terminal renal insufficiency. Humoral immunity produced less significant results: the B lymphocyte count and serum immunoglobulins were normal; only C3 levels were found below normal range. Thus it would seem that cell-mediated immunodeficiency appears in an early stage of chronic renal failure and that hemodialysis does not improve this deficiency.