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A review of the literature provides evidence indicating that lactose malabsorption and lactose intolerance are different though correlated phenotypes, with a high proportion of malabsorbers being tolerant and a relatively small proportion of absorbers being intolerant. Support for the belief that either absorption or tolerance is controlled by a single gene pair is not strong, either when racial/ethnic differences in absorption/tolerance are examined or when studies of racially mixed populations have been conducted. Evidence does support the belief that absorption is controlled by a single gene pair when families of northern European ancestry are examined. Tolerance, but probably not absorption, appears to be influenced by dietary practices. We suggest that social policy involving the use of milk and other dairy products in food supplement programs directed at non-white populations should be guided by data concerning tolerance, not absorption.