The objective of this study was to investigate the effect of massage therapy on phase adjustment of rest-activity and melatonin secretion rhythms to the nocturnal period in full-term infants. Rest-activity cycles of infants (measurement 1, n = 16) were measured by actigraphy before and after 14 days of massage therapy (starting at age 10 [+/-4] d) and subsequently at 6 and 8 weeks of age. 6-Sulphatoxymelatonin excretion was assessed in urine samples at 6, 8, and 12 weeks of age (measurement 2, n = 21). At 8 weeks the controls revealed one peak of activity at approximately 12 midnight (11 p.m.-3 a.m.) and another one at approximately 12 noon (11 a.m.-3 p.m.), whereas in the treated group, a major peak was early in the morning (3 a.m.-7 a.m.) and a secondary peak in the late afternoon (3 p.m.-7 p.m.). At 12 weeks, nocturnal 6-sulphatoxymelatonin excretions were significantly higher in the treated infants (1346.38 +/- 209.40 microg/night vs 823.25 +/- 121.25 microg/night, respectively; <.05). It is concluded that massage therapy by mothers in the perinatal period serves as a strong time cue, enhancing coordination of the developing circadian system with environmental cues.