Exercise-induced asthma (EIA) is one of the major factors that affect optimal performance in sport. The prevalence of EIA is reported to be on the increase among school children worldwide. The aim of this study was to indicate EIA prevalence among primary-school children in South Africa. A field study determined the prevalence of EIA. A convenience sample of 127 children aged 8 to 16 years was selected. A health- screening questionnaire was used. The criteria for selection were that the subjects should be non- asthmatics and should not have any other illness during the screening that could interfere with the results. Peak expiratory flow rate (PEFR) was measured pre- and post-exercise using an ASSESS peak flow meter. The subjects did a six-minute run on a school playground. The post-exercise PEFR was measured within 10 minutes of exercise. The determinant of EIA was ≥ 10% decrease in PEFR after exercise. A total of 112 (88%) subjects participated in the study. Fifteen subjects were excluded (eight had asthma, five had respiratory tract infection and two had other illnesses). The average exercise heart rate was ± 80% of predicted maximal heart rate. The prevalence of EIA was 23% (n = 26). The incidence of a history of allergic rhinitis was statistically significantly increased among those with positive tests (p = 0.027). This study highlights the need to screen all children so that EIA can be determined and addressed appropriately.