In 37 full-term and preterm infants periodic oscillations of skin blood flux were studied by means of laser Doppler technique during the first week of life. The development of rhythmic oscillations of skin blood flux was similar in all infants. On the first postnatal day rhythmic oscillations were present in the heel skin of all full-term and preterm infants, but were rarely observed in the back and thigh skin. These flux motion patterns were not influenced by small changes in skin temperature. On day 4 rhythmic oscillations became predominant in all body regions. The oscillation frequencies of blood flux in the back, thigh and heel skin of full-term neonates reached the lower range of adult values at the end of the first postnatal week, whereas the oscillation frequencies in the preterm infants were still below the range of full-term neonates.