Middle molecules can act on several levels of uremic disease. So, this work is a multidisciplinary one with the participation of nephrologists, hematologists and also pharmacologists, chemists and biophysicians. We present here our results on four different toxic effects found with middle molecules: the energy dependant phenomena, the platelet aggregability, the cardiotoxic, and the neurotoxic effects. Middle molecules were isolated from urine of normal subjects and blood of patients with chronic renal insufficiency and treated by hemodialysis. Separation was done according to Furst's procedure.