Insulin-like growth factor binding protein-1 (IGFBP-1) is a major protein in amniotic fluid. In this study, we evaluated the diagnostic potential of IGFBP-1 measurement in cervical/vaginal secretions as an indicator of ruptured fetal membranes. Data were also compared with those obtained by the ROM-check Membrane Immunoassay (Adeza Biochemical, Sunnyvale, California) that is based on the detection of fetal fibronectin in vaginal fluid. In women with intact membranes and not in labor, the concentration of IGFBP-1 in specimens obtained from the cervix and immersed in 0.5 ml of assay buffer ranged from < 0.5 to 90 micrograms/l, whereas in specimens obtained less than 8 h after spontaneous or artificial rupture of membranes it varied between 175 and 20,000 micrograms/l, the median being 1,900 micrograms/l. The values greater than 100 micrograms/l were interpreted as containing amniotic fluid. The IGFBP-1 measurement and the ROM-check Membrane Immunoassay were carried out parallel in the vaginal swab specimens obtained from 54 pregnant women from 1 h to 1 week after the rupture. Twenty-four women had ROM confirmed from 1 h to 1 week earlier. In this group of patients, IGFBP-1 concentration > 100 micrograms/l had a sensitivity of 75% and a specificity of 97% in diagnosis of ROM. The corresponding numbers for a positive ROM-check were 92% and 80%. The positive predictive value was 95% for the IGFBP-1 measurement compared to 79% for the ROM-check test.(ABSTRACT TRUNCATED AT 250 WORDS)