OBJECTIVE Since maternal smoking causes fetal circulatory abnormalities, as well as disturbances of the maternal endocrine equilibrium, we measured the PRL, hGH and insulin-like growth factor-I (IGF-I) concentrations in the cord and venous blood of neonates of smoking mothers to determine whether or not the tobacco smoke affects the endocrine status of the neonate. METHODS The above hormones were measured in the cord blood of the newborns of both smoking and non-smoking mothers. Also, PRL and hGH were determined at 24 and 72 hours after birth in newborns of both groups. METHODS Fifty-three newborns of smoking and 47 newborns of non-smoking mothers were investigated. Seventeen of the newborns of the smoking and 21 of the non-smoking mothers were preterm. The remainder were full-term. METHODS PRL was measured with a solid-phase immunoradiometric assay, hGH with a solid-phase two-site immunoradiometric assay and IGF-I with a solid-phase radioimmunoassay after extraction with acid-ethanol. RESULTS The median value of PRL in the 17 preterm newborns of smoking mothers was 4941 mU/I (range 1322-7230), whereas in the 21 preterm newborns of non-smoking mothers it was 2013 mU/I (range 243-4740) (P = 0.0002). The median hGH value in the above subjects was 102.0 mU/I (range 35.2-208.4) and 59.8 mU/I (range 11.6-134.2), respectively (P = 0.0039). The median IGF-I was 580.7 U/I (range 253.2-4851.1) and 530.6 U/I (range 239.6-3591.5), respectively (P = 0.429). In the 36 full-term newborns of smoking mothers the median PRL value was 5171 mU/I (range 2074-7530), whereas in the 26 full-term newborns of non-smoking mothers it was 5081 (range 244-6540) (P = 0.048). The median hGH was 69.6 mU/I (range 42.3-280.0) and 32.2 mU/I (range 6.2-200.0), respectively (P = 0.0031). Also, the median IGF-I value was 926.3 U/I (range 348.5-5344.7) and 462.1 U/I (range 250.2-1578.7), respectively (P = 0.0024). On the 3rd day the PRL in the preterm neonates of both smoking and non-smoking mothers showed the same 16.5% drop, and thus the difference between the groups was maintained. A similar reduction in the hormone levels was observed in the full term neonates. CONCLUSIONS The findings indicate that the maternal tobacco-smoking causes disturbances of the endocrine status of the fetus, as shown by the increased levels of PRL, hGH and IGF-I, which are more pronounced between 30 and 37 weeks of gestation than at term.