Rhinovirus (RV) colds are associated with asthma exacerbations and experimental infections are commonly used to investigate the mechanisms involved. However, a temporal association between experimental RV infections and falls in peak expiratory flow (PEF) have not been demonstrated. PEF was measured in 22 volunteers (11 normal, five atopic, six atopic asthmatic) who developed RV serotype 16 colds after inoculation. PEF was measured twice daily for 2 weeks prior and 6 weeks after RV infection and episodes of respiratory morbidity based on changes in PEF were defined using validated criteria. Six significant reductions in PEF were temporally related to the RV infections (in two (18%) normal, one (20%) atopic, three (50%) atopic asthmatic subjects, p=0.1) and occurred 4-9 days (median 6) after inoculation. Mean+/-SEM PEF at day 6 was 87.8+/-1.8% of the predicted value in the six subjects with reductions versus 99.4+/-1.4% pred in those without (p=0.01). Symptom scores were significantly different at day 6 in the two groups (10.6+/-1.9 versus 6.8+/-1.0, p=0.03), but no differences were noted in the viral culture scores and changes in nasal albumin. In subjects with significant PEF reduction, the decrease in the provocative concentration causing a 20% fall in the forced expiratory volume in one second (FEV1) (PC20) was 1.7+/-1.3 mg x mL(-1) versus 1.2+/-1.1 mg x mL(-1) in the negative group (p=0.06). The degree of seroconversion to RV was significantly higher in the group with reduced PEF (median change dilutions 8 versus 4, p=0.02). The results of the present study suggest that rhinovirus-associated, respiratory morbidity occurs during experimental infection in some but not all normal and asthmatic subjects and also that experimental colds are a valid model for the study of rhinovirus-associated airway symptoms and asthma exacerbations.