The purpose of this study was to establish reference ranges for numerical fetal heart rate (FHR) data in postterm pregnancy and to compare them with the patterns of fetuses under undisturbed condition at term. FHR was analysed on-line by Sonicaid Computer System 8000. A statistically significant decrease in the number of accelerations and decrease of variation in postterm pregnancy was observed. The duration of high variation (high episodes) in the 42nd week of gestation was statistically lower than in the pregnancy at term. These observations should be taken into account by clinicians in the interpretation of FHR records in postterm pregnancy.