A prospective study was carried out to establish the influence of deteriorated metabolism of glucose in mothers to the synthesis and secretion of prolactin during the pregnancy. The examination included a 101 pregnant women with delivery term between 259 and 287 day of gestation; 36 pregnant women manifested glucose intolerance or diabetes during the pregnancy and 12 of them also had marked signs of gestation. Control group consisted of 65 pregnant women. The level of prolactin in the sera of mothers with glucose intolerance (205.7 +/- 66.4 micrograms/l) was significantly increased (p < 0.05) than in case of mothers with normal pregnancy (172.2 +/- 60.7 micrograms/l), probably due to the development of gestosis in a large number of pregnant women. The difference of prolactin level in pregnant women with glucose intolerance but without the elements of gestosis (167.3 +/- 35.7 micrograms/l) and in women with normal pregnancy was not important. The difference of prolactin level in the serum of umbilical artery (245.5 +/- 101.2 micrograms/l and 261.0 +/- 78.8 micrograms/l) and in amniotic fluid (428.6 +/- 161.1 micrograms/l and 422.9 +/- 112.9 micrograms/l) was not of statistical significance. Pregnant women with glucose intolerance and elements of gestosis had significantly higher concentration (p < 0.05) in the serum of the mother, in the serum of umbilical artery and in the serum of amniotic fluid (282.4 +/- 41.6 micrograms/l, 315.6 +/- 103.3 micrograms/l and 460.4 +/- 130.2 micrograms/l) than the pregnant women with glucose intolerance but without elements of developing gestosis (167.3 +/- 35.7 micrograms/l, 210.5 +/- 81.5 micrograms/l, and 402.6 +/- 118.8 micrograms/l). There was no evidence of the functional connection between prolactin and glucose metabolism.