ABSTRACT Simultaneous measurements of placental cystine-aminopeptidase ("plasma oxytocinase") (P-CAP) and total urinary oestrogens were performed in pregnancies complicated with essential hypertension, mild or severe preeclampsia. Essential hypertension (n = 31): Neither the enzyme activity nor the urinary output of oestrogens were significantly reduced in these cases. Mild pre-eclampsia (n = 59). In this group of patients a significant reduction of the 2 parameters was observed (P-CAP: P < 0.001; total oestrogens: 0.02 < P < 0.05). Expressed in per cent of the normal mean the P-CAP and and total urinary oestrogens were 71.0 and 83.2 per cent, respectively. Severe pre-eclampsia (n = 41): A more marked reduction both in P-CAP (P < 0.001) and total urinary oestrogens (P < 0.001) was observed in this group. The percentage reduction from the normal mean of P-CAP and total urinary oestrogens was 46.0 and 35.2 per cent, respectively. In the whole material (n = 131), including both essential hypertension and pre-eclampsia, secondarily retarded foetal growth was found in 39 pregnancies. The percentage reduction from the normal mean of both P-CAP and total prinary oestrogens in this group was 46.0 and 53.2 per cent, respectively. In 12 cases with a low placental coefficient (placental weight: infant weight) the P-CAP was 41.7 per cent and the total urinary oestrogen excretion 74.6 per cent of the normal mean. When evaluating such cases, simultaneous measurements of P-CAP as a placental function test and the urinary output of oestrogens as a foeto-placental function test, might be beneficial. In each of 4 cases of intra-uterine foetal death the P-CAP values were below 2.5 percentile of the normal pattern. The total urinary oestrogen levels, however, showed a more diffuse pattern and in 1 case the levels were within the normal range.