Schoolchildren (n= 473), 12–13 years of age, from five schools, and without known asthma, participated in a screening test for exercise-induced asthma (E1A). The children were tested in large groups of 10–15 pupils. Peak expiratory flow (PEF) was measured before, immediately after, and 6–8 min after 6 min of running exercises in a gymnasium. A fall in PEF of at least 10% on two separate test occasions was considered an abnormal result. Children with abnormal results were given an asthma questionnaire and then tested individually in hospital with a standardized exercise test measuring FEVb PEF, and flow/volume curve. In the screening test, 23 (4.9%) of the 473 children had an abnormal result. When tested in hospital, five (1%) children had a decrease in PEF and/or FEV, of at least 10% (10–14%) after exercise. Furthermore, three of these five children had a history indicating mild EIA. We conclude that the use of PEF measurement as a screening method for EIA in large groups of schoolchildren cannot be recommended because it yields many false-positive results.