The aim of this study was to clarify the link between M. pneumoniae and asthma. This study was carried out on 57 asthmatic children, 6-14 years old : Group 1 of 32 chronic stable asthmatics and Group 2 of 25 chronic asthmatics in exacerbations. IgG anti-M.pneumoniae antibody index (ABI) was measured using ELISA. In group 1, 25% of patients were positive while in group 2, 24% were positive. Also, in group 2, 17 patients had a second follow-up serum sample and a significant change in ABI was found in 23.5% of them. ABI in asthmatics was significantly higher than controls. This suggests that M. pneumoniae may have a role in initiation and persistence of asthma as well as in asthma exacerbations.