We examined how chronic respiratory symptoms, reported in a questionnaire, and results of skin prick tests and spirometry predicted variability in peak expiratory flow (PEF) among 6-12-yr-old children (n = 1,854). After characterization with skin tests and spirometry, children were followed for 2-3 mo during the winter of 1993-1994. Peak expiratory flow was measured daily in the morning and evenings. Children with asthmatic symptoms (wheeze and/or attacks of shortness of breath with wheeze in the past 12 mo and/or ever doctor diagnosed asthma) had a greater variation in PEF than children with dry nocturnal cough as their only chronic respiratory symptom. Similarly, doctor-diagnosed asthma was associated with a greater variation in PEF, also among children with asthmatic symptoms. Peak flow variability increased with an increasing number of symptoms reported in the questionnaire. Atopy, positive skin test reactions to house dust mite and cat and lowered level (as % of predicted) in FEV1 and in MMEF were also associated with an increased variation in PEF. All the differences were observed in both diurnal and day-to-day variation in PEF. In conclusion, chronic respiratory symptoms reported in a questionnaire, spirometric lung function and skin prick test results among asthmatic children predicted variation in PEF measured during a 2-3 mo follow-up. The difference in morning PEF coefficient of variation (CV) between children with asthmatic symptoms and children with cough only was somewhat bigger in girls than in boys. The effect of atopy on morning PEF CV was somewhat bigger in young than in older children.