There is a growing evidence that chlamydia pneumoniae may participate in asthma inflammation and acts as a co-factor in asthmatic episodes.This study was conducted on 30 asthmatic patients together with 20 healthy volunteers as a control group.This study was done to evaluate the incidence of C.pneumoniae infection in asthmatic patients and to study the association between C.pneumoniae IgG and the severity of asthma.All cases were subjected to full history taking, through clinical examination, plain chest X-ray, ventilcetory function before and 20 minutes after 2 puffs of salbutamal and estimation of C.pneumoniae IgG in the serum by MIF technique.The result of the study support the hypothesis about the role of Chlamydial infection in the etiopathogenesis of asthma.