OBJECTIVE This study investigated the role of the fat content of milk on symptoms of lactose intolerance. METHODS Subjects recorded intolerance symptoms using a visual analogue scale (VAS) following ingestion of three test milks for varying fat content for a two-day period. METHODS The subjects were thirty adult volunteers, patients of two Estonian out-patient clinics with diagnosed lactose intolerance. The study milks were drunk at home or at work. All thirty subjects completed the study protocol. METHODS Each subject drank, in random order, fat-free milk (4.9% lactose), high-fat milk (8% fat, 4.9% lactose), and a lactose-free and fat-free control milk. They drank 200 ml of the milk twice a day for two days, one milk type per session, with five days between sessions. The subjects noted their gastrointestinal symptoms during the test periods and during a 5 d milk-free period at the beginning of the study. The occurrence and severity of symptoms were compared. A global measure of the severity of symptoms was defined by computing the sum of the symptoms scores. RESULTS The sum of symptoms was higher during all milk periods than during the milk-free period (P < 0.01). There were no statistically significant differences in the occurrence or severity of symptoms during the fat-free milk period compared with the high-fat milk period. CONCLUSIONS Even a marked difference in the fat content of milk did not affect the symptoms of lactose intolerance. Consequently, there seems to be no case for recommending full-fat milk products in the treatment of lactose intolerance.