The effect of pregnancy on maternal serum total cortisol (MSFT) was studied systematically in the course of 90 normal pregnancies (n = 204). Moreover, the evaluation of MSFT determinations in abnormal pregnancies, intrauterine growth retardation (IUGR) and obstetrical complications, premature rupture of the membranes (PROM), premature delivery (PD), and full term pregnancies with post maturity syndrome (PMS) were also investigated. MSFT was measured by an enzyme immunoassay. Gradual increase in MSFT was found from the 6th week of pregnancy to the 40th week of pregnancy and a sharp rise was noted during the last 2 weeks before the onset of labor (P < 0.002). In IUGR, MSFT was significantly lower (P < 0.001). In the cases of PROM and PD, MSFT was highly elevated (P < 0.0001), independently of the gestational age. In pregnancies with well documented PMS, MSFT was much lower than in normal full term pregnancies with even a downward trend in serial determinations (P < 0.0001). © 1990.