The normal range of serum cystine-amino-peptidase (C.A.P.) in 54 cases of uncomplicated pregnancies was established. 21 patients whose pregnancies were though to be "at risk" were serially monitored by sonar biparietal cephalometry and serum cystine-amino-peptidase determination. The results show that exists a correlation between C.A.P. and biparietal cephalometry values. Furthermore the "predictive power" towards neonatal conditions (by birth weight and Apgar score determination) was of 77,55% for the biparietal cephalometry and 76,10% for C.A.P.