On the basis of the results of serial enzyme and cytohormonal assays in the last lunar month of gestation in 232 pergnant patients with high-risk pregnancy, it has been shown that the "at term" and inflammatory smears, which persist for over five days before labor, and post-partum" smears, significantly correlate with abnormal (low or decreasing) results of serum placental cystine aminopeptidase activity and with the pathologic course of pregnancy and labor as well as with the poor neonates' condition. The average serum placental and tissue cystine aminopeptidase determinations were the lowest in women with "post-partum" smears or persisting "at term" smears. These activities reached their highest they temporarily decreased. The oxytocinase activity curves in women with cytolytic smears were similar to those in patients with the "before term" smear patterns, which persisted before delivery. The average oxytocinase activity in women with the inflammatory smears was at first the highest and later it decreased most rapidly of all the groups under consideration. The maternal serum alkaline phosphatase and its heat-stable fraction in pregnant patients with "post-partum" and persisting "at term" smears were at first the lowest and just before labor the highest of all the cytologic pregnancy patterns. Colpocytograms confirmed their high prognostic value when compared with the enzyme tests of placental function.