The onset of stool passage, timing of transition to yellow stools and the pattern of stooling frequency over the first 4 weeks were studied in infants < 1500 g at birth. The time of passage of the first stool (median, 19) correlated with birth weight and gestational age but not with presence or severity of respiratory distress; fourteen percent passed stool after 1st 48 hours. Transition to yellow occurred at 17.6 +/- 6.4 days and was related to the onset of feeding and birth weight. Stooling frequency was similar in Wk 2 as Wk 1, increased in Wk 3 and plateaued on Wk 4. Volume of feeding/day increased each week over that of preceding week but stooling frequency was not related to the increased volume or any of the other variables.