Serum angiotensin I-converting enzyme activity (SCEA) was investigated in 15 healthy premature (gestational age ranging from 30 to 36 weeks) and in 14 healthy full-term (gestational age ranging from 37 to 41 weeks) newborns as well as in 16 healthy adults (32.0 +/- 2.6 years). SCEA mean values in the three groups, respectively, 23.3 +/- 1.3, 24.4 +/- 1.6 and 23.2 +/- 1.7 nM . min-1 . ml-1, did not differ significantly from each other and in the newborns there was no correlation between SCEA values and gestational age.