The aim of this study was to search for the existence of behavioural states in the human fetus and to describe their developmental course. In a longitudinal study, 14 low-risk fetuses were studied at 2-week intervals from 32 weeks of gestation onward. Fetal body movements as well as fetal eye movements, visualized by means of real-time ultrasonic imaging, and fetal heart rate patterns, recorded by means of a cardiotocograph, were used as state variables. At 38 and 40 weeks, four distinct behavioural states, named states 1F through 4F and corresponding respectively to states 1 through 4 of the neonate, could be identified. That these constellations of parameters represented true behavioural states was demonstrated by the stability of association of parameters for prolonged periods and by the simultaneity of change of parameters at state transitions. There is evidence for episodes of wakefulness in the fetus. Before 36 weeks, cycles were present in each of the state variables and combinations of parameters typical of particular states were observed. However, the relatively short durations of these combinations and the lack of simultaneity of change in the three state variables support the conclusion that these periods of coincidence occurred by chance and did not represent organized behavioural states.