We have shown that there is a relation between allergy to cow's milk and chronic sleeplessness in infants. In the present report we describe the sleep characteristics of children with allergy-related sleep disruption. We compared the polygraphic characteristics of nine infants studied before and after the exclusion of milk from the diet. The infants had a mean age of 18.3 +/- 13.3 and 25.4 +/- 12.7 weeks at the first and the second recording, respectively. Diagnosis of allergy was based on clinical observation. Sleep normalized after milk was withdrawn, deteriorated after a challenge with milk, and normalized again on a second trial of milk elimination. Before the change in diet, the infants' polygraphic recording showed frequent arousals (8-22), short sleep cycles, and a large amount of NREM1 sleep. Gastroesophageal reflux and sleep apnea were not responsible for the sleep fragmentation. After milk was excluded from the diet for 7 weeks, the infants showed striking changes in sleep quality. There was a significant decrease in number of arousals (-41.7%) and an increase in total sleep time (+22.7%) and in NREM2 and 3 sleep (+387.9%). NREM1 sleep decreased significantly (-42.1%). During the second recordings, these sleep values could not be distinguished from those of 40 age-matched controls studied in the same laboratory environments. We do not know if the observed modifications in sleep could reflect immunologic changes within the central nervous system.