The aim of this study was to investigate the availability of vaginal resistance values to estimate early pregnancy in heifers and cows on days 18-21 post-insemination. Seven Brown Swiss cows and ten heifers without any palpable reproductive disorders were used. Cloprostenol, a synthetic analogue of PGF(2 alpha), was administered intramuscularly twice (500 mu g) 11-days apart. After second cloprostenol administration, animals were observed for the overt signs oestrus and, inseminated twice with frozen semen after confirmation of oestrus by rectal palpation. Electrical conductivity of vaginal mucosa was measured through ventral wall of vagina adjacent to caudal end of cervix uteri by a handy-held instrument. Vaginal conductance of animals was measured twice, with a 12 h interval, on days 0 (day of oestrus), 3, 6, 10, 11 19 20 and 21 in cows, and on days 0 (day of oestrus), 3, 6, 10, 13, 18, 19 and 20 in heifers. To estimate plasma progesterone levels, jugular blood samples (10 mL) were also collected on days 19, 20 and 21 for cows, and 18, 19 and 20 for heifers. Pregnant animals were detected by rectal palpation 60 days after insemination. In pregnant cows, electrical resistance of vaginal mucosa measured between days 19-21 was significantly higher than non-pregnant animals, while vaginal resistance values determined on the day of insemination, and on days 3, 6, 10 and 13 post-insemination were similar in both groups. Likewise, vaginal impedance readings in pregnant heifers determined between days 18-20 were significantly higher than those non-pregnant animals. Vaginal resistance measurements in cows (between days 19-21) and heifers (between days 18-20) were significantly correlated with plasma progesterone concentrations both in pregnant and non-pregnant groups. It was concluded that vaginal resistance values might be used for the diagnosis of early pregnancy as a contributor or predictor method in cows and heifers.