The aim of this study is the evaluation of the reliability of vaginal fluid (VF) prolactin (PRL) for detecting prematurely ruptured membranes (PROM) and the comparison of this marker with vaginal fluid alpha-fetoprotein (AFP) and placental lactogen (HPL). In 21 pregnant women with recent or prolonged PROM from 20 to 41 weeks' gestation, in whom intact membranes were never found subsequently VF- and MS-PRL, -AFP and -HPL were measured by enzyme immunoassays, which are sensitive and very rapid. The same markers were also measured in MS, VF and urine samples (U) in 12 pregnant women of the same gestational age, without PROM, in whom the membranes were ruptured later during labor. In PROM, independently of prematurity and duration of PROM VF-PRL levels were significantly higher (2-10-fold) than the paired MS-PRL (p less than 0.0001) and ranged from 130 to 2315 ng/ml. In contrast, VF-PRL and urine PRL concentrations in pregnancies without PROM were very low or undetectable (range: 0-5 ng/ml and 0.15-1 ng/ml, respectively). Vaginal fluid AFP values in PROM from 20th to the 33rd week of pregnancy were significantly higher (5-50-fold) than the paired MS-AFP (p less than 0.01) and ranged from 103 to 5500 ng/ml. In PROM after the 33rd week of pregnancy, VF-AFP values were either lower (1/3), or equal to, or even higher (up to 2-fold) than MS-PRL. On the contrary in pregnancies with intact membranes, VF-AFP were always less than 9 ng/ml and urine AFP was undetectable (range: 0.2-1.1 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)