The prevalence of lactose intolerance as revealed by the standard lactose tolerance test was compared with the occurrence of intolerance to graded amounts of milk in 69 black and 30 white children. Of the black children studied, 11% of those 4 to 5 years old, 50% of those 6 to 7 years old, and 72% of those 8 to 9 years old were found to be lactose-intolerant, yet no child was intolerant to 240 ml of milk. Symptom responses to greater amounts of milk did not suggest that the frequency of primary lactose intolerance might be a reason for limiting existing milk programs for young children. No significant differences were found between the milk intakes of black lactose-tolerant and black lactose-intolerant children, nor between milk intakes of 6- and 7-year-old black and white children in Boston. However, 8- to 9-year-old black children drank significantly less milk than 8- to 9-year-old white children did. The blood glucose response at 0, 20, and 45 min after the ingestion of 2 g lactose/kg (maximum 50 g) was unreliable as an indicator of an individual's symptomatic response to lactose.