The serum HPL level was studied in normal and high-risk pregnancies. 30 patients with premature labour showed significantly decreased levels. In 24 patients with monosymptomatic toxaemia, HPL patterns showed a statistically significant deviation from the normal standard curve; a highly significant decrease was observed in 23 cases of polysymptomatic gestoses. As opposed to the results of other authors, no significant difference from the normal distribution of HPL was found in cases of Rh sensitisation (13 patients) and diabetes mellitus (16 patients). A noteworthy results was seen in 19 cases of cervix insufficiency: after purse-string suturing of the cervix (original method of Shirodkar), the previously low plasma HPL level rapidly rose to normal levels. Because of the small number of cases without an adequate control group this phenomenon cannot be attributed with certainly, as yet, to the cerclage procedure.