Spectral analysis of spontaneous fluctuations in human fetal movement revealed strong oscillations at frequencies between 0.24 and 0.90 cycle per minute, which are much higher than those of the cyclic alternation of quiet and active states in the fetus and neonate. Oscillations at frequencies up to 2.88 cycles per minute were also detected, but they were usually much weaker. The prominent peaks in the fetal movement spectra are in the frequency range of recently reported neonatal motor rhythms, and indicate the existence of a cyclic process controlling spontaneous motor output that oscillates near one cycle per minute and begins to function in utero.