The role of Chlamydia pneumoniae in asthma has drawn much attention in recent years. In this study we assessed the prevalence of C. pneumoniae infections in patients with chronic stable and acute exacerbation of asthma and compared it with normal population. Twenty adult patients with chronic stable asthma and 21 patients with acute exacerbations of asthma and 41 matched control subjects were studied for presence of C. pneumoniae using cell culture. This study suggests that positive results of C. pneumoniae culture are associated with both chronic stable and acute exacerbation of asthma. It could be concluded that C. pneumoniae is a risk factor for either development or exacerbation of asthma.