Reference values for creatinine in serum were established using a fully enzymatic method, adapted to a discontinuous analyzer. Our reference group included 250 females and 215 males (blood donors, hospital staff and patients) aged 18-70 years. Up to 60 years, creatinine concentration did not depend on age, but there was a significant difference between the creatinine concentrations of women and men. We propose reference ranges for creatinine in serum (95% range) of 44-80 mu mol/l for women and of 44-97 mu mol/l for men.