Day-sleep polygraphic recordings were performed in 10 normal infants and 10 siblings of infants who died of sudden infant death syndrome. Body movements were studied in both groups of infants during 3 stages of sleep. In controls and siblings, the mean number of body movements per sleep hour, per infant was respectively 7 or 6 in quiet sleep and 22 and 23 in REM sleep; the mean duration of body movement was longer (11.3 sec) in REM sleep than in non-REM sleep (9.4 sec). In both cases, there was no significant difference between the 2 groups. An analysis of the movement duration showed that most of them lasted between 5 and 10 sec and in siblings were statistically more numerous during indeterminate sleep. In both groups, these movements appeared more often at the beginning and at the end of the quiet sleep, but were more equally distributed in the REM sleep. Respectively 15 and 13.7% of these movements in the normal and sibling group were accompanied by a brief respiratory pause. The relation between body movements and sleep is discussed.