Objective: This study investigated the role of the fat content of milk on symptoms of lactose intolerance. Design: Subjects recorded intolerance symptoms using a visual analogue scale (VAS) following ingestion of three test milks of varying fat content for a two-day period. Subjects/Setting: 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. Intervention: 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 ®ve 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 de®ned by computing the sum of the symptom 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 signi®cant 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. Sponsorship: The study was supported by the Foundation of the Finnish Association of Agronomists: Valio Ltd, Finland, provided the test milks.