The urinary estriol values of a morning sample determined by a new semiquantitative method was correlated with the total 24 hour estriol excretion determined by colorimetric method on patients with normal and pathologic pregnancy. The correlation coefficient, calculated on 240 assays operated on urine samples obtained from 70 normal pregnant women, is highly significant statistically (P less than 0.001). The profiles of the serial assays, obtained by these two procedures on patients with pathologic pregnancy, show a very strong analogy. The Authors believe that such a method, just for its simple and rapid realization, may be applied alternatively to RIA assay or colorimetric method for the cases which are believed to be in need of rapid evaluation of estriol and/or when another method is unfeasible.