Although the prevalence of lactose malabsorption is high and the importance of this diagnosis is established in gastroenterological practice, still a variety of poorly standardized tests is used to investigate the ability of the small bowel to digest lactose. In this report the various most commonly used lactose malabsorption tests are described and compared with each other knowing that a 'gold standard' does not exist. The hydrogen breath test is the test most used in clinical practice. On the basis of recent investigations the recommendation is made to improve the accuracy of this test by prolonging it to 4 hours and by simultaneous measuring of the oro-coecal transit time.