An important feature of "asthma" in children is the occurrence of repeated episodes of airflow obstruction lasting days or weeks. In this 1-yr longitudinal study, we investigated the nature of these episodes and their relationship to other indices of asthma. A random sample of children aged 7 and 8 yr reporting either cough or wheeze was invited to attend for skin testing. Ninety-six atopic children, half with cough and half with wheeze, and 96 nonatopic children, again half with cough and half with wheeze, were selected to join a longitudinal study. All children recorded twice daily peak expiratory flow (PEF) measurements and a daily 10-point symptom score. One hundred eighty-three children (95.3%) successfully completed the study. Episodes of respiratory morbidity, defined as falls in PEF to less than 1.5 standard deviations (SD) below subject mean lasting for more than 2 days, were identified and the 642 resulting episodes examined. Episodes were more common in autumn and winter (p = 0.003 to 0.017). The mean number of episodes per child was 3.5 (range 0 to 8): 94 (51.4%) children experienced more than three episodes, 54 (30.0%) experiencing five or more. The average duration of episodes was 4.1 days (range 2 to 27 days), with 44 (24%) subjects demonstrating episodes of average duration of 5 days or more and 18 (10%) of greater than 7 days. Episodes were more severe in children with wheeze (p = 0.013) and slightly more frequent in those with cough alone (p < 0.05). Atopy had no effect on episode frequency, duration, or magnitude.