Pregnancy zone protein (PZP) and alpha 2-macroglobulin (alpha 2M) serum concentrations were studied in healthy female donors, in women suffering from benign and malignant breast tumours, and in relation to normal and abnormal pregnancies. PZP was found to be useless as a tumour marker. Thus, PZP levels in breast cancer patients did not differ from those of fibroadenoma patients or healthy women. There was no correlation between PZP (or alpha 2M) concentrations and the pTNM-classification or metastatic burden of the breast cancer patients. Moreover, PZP levels were unaffected by cancer treatment and the course of disease. Neither patients nor control donors showed any age-dependent increase in circulating PZP and the mean serum value (8.38 +/- 4.83 mg/l, mean +/- SD) determined in a population of 154 non-pregnant women was considerably lower than that of most previous reports. Serum concentrations were unchanged during the normal menstrual cycle, but increased during pregnancy. However, late pregnancy sera (35th gestational week) contained significantly less PZP than previously reported by others, and non-pregnancy levels were observed in one out of 22 cases. Results obtained in hydatidiform mole patients were similar to findings in normal pregnancy. Neither serum 17 beta-oestradiol nor morphological differentiation between complete and partial mole showed any correlation with circulting PZP levels. Apart from a moderate increase during gestation, alpha 2M concentrations showed little variation between the populations examined.