This study investigates the role of respiratory viruses in exacerbations of asthma in adults. A longitudinal study was conducted on 138 adults with asthma, aged 19-46 years, over a period from October 1990 to August 1992. The study found that 80% of symptomatic colds were associated with asthma symptoms, and 89% of colds were linked to asthma exacerbations. Laboratory-confirmed respiratory tract infections were identified in 229 episodes, with 24% associated with a significant reduction in peak expiratory flow rate (≥50 l/min) and 48% with a decrease of ≥25 l/min. Rhinoviruses, coronaviruses, influenza B, respiratory syncytial virus, parainfluenza virus, and chlamydia were all associated with objective evidence of asthma exacerbations. The findings suggest that respiratory virus infections commonly cause or are associated with exacerbations of asthma in adults, highlighting the importance of recognizing and managing these infections in asthmatic patients.This study investigates the role of respiratory viruses in exacerbations of asthma in adults. A longitudinal study was conducted on 138 adults with asthma, aged 19-46 years, over a period from October 1990 to August 1992. The study found that 80% of symptomatic colds were associated with asthma symptoms, and 89% of colds were linked to asthma exacerbations. Laboratory-confirmed respiratory tract infections were identified in 229 episodes, with 24% associated with a significant reduction in peak expiratory flow rate (≥50 l/min) and 48% with a decrease of ≥25 l/min. Rhinoviruses, coronaviruses, influenza B, respiratory syncytial virus, parainfluenza virus, and chlamydia were all associated with objective evidence of asthma exacerbations. The findings suggest that respiratory virus infections commonly cause or are associated with exacerbations of asthma in adults, highlighting the importance of recognizing and managing these infections in asthmatic patients.