The determination of the activity of alkaline phosphatase (AP)--orthophosphate-monoesterphosphohydrolase, EC.3.1.3.1.--and alanine-aminopeptidase (ANA)--alpha-aminoacyl-peptide hydrolase (microsomal), EC.3.4.11.2--in the serum of non-gravid and gravid women has shown that in non-gravid women normal ANA values range from 17.0 to 32.0 I. U. and normal AP values from 14.4 to 26.0 I. U., the ANA/AP quotient amounting to 1.28 (S = +/- 0.301 I. U., KV = 23.5%, n = 29). The determination of the activity of the above quoted enzymes has shown that in the course of pregnancy the values of both enzymes increased by the exponential curve which allowed the calculation of the ANA/AP quotient for each month of pregnancy. The ANA/AP quotient determined in this way is proposed to serve as a diagnostic parameter in the routine control of pregnant women.