Objective To investigate the infection rate of Legionella pneumophila(LP)in children younger than 5 years with lower respiratory infections by ELISA and PCR.Method Serum LP-IgM and IgG were measured by ELISA,and LP DNA in sputum or throat swab were detected by PCR in 300 children less than 5 years with lower respiratory infections.The data were analyzed by chi-square test and the consistency of the two methods was analyzea by NcNemar test.Results Serum antibody detected by ELISA was positive in 17 cases(5.67%),including 10 positive of IgM and 7 positiile of lgG.In these 17 eases,11 were males and 6 were females with similar positive rates(5.76%vs 5.5%).Four cases(2.53%)were positive in children aged from 27 days to 1 year,while 7(7.37%)and 6 cases(12.77%)were positive in children aged 1-3 years and 3-5 years,respectively.Seven cases(5.19%)found in the winter and spring seasons and 10 cases(6.06%)in summer and autumn seasons.Eleven children(11.83%)were from urban area and only 6(2.9%)from countryside.DNA in sputum or throat swab detected by PCR was positive in 16 cases(5.33%),included 10 males and 6 females with similar positive rates(5.24%vs 5.5%).Five cases(3.16%)were positive in children aged from 27 days to 1 year,while 6(6.32%)and 5 cases(10.64%)were positive in children aged 1-3 years and 3-5 years,respectively.Three cases(2.22%)found in the winter and spring seasons and 13 cases(7.88%)in sunmmr and alltumll seasons.Nine children(9.68%)were from urban area and only 7(3.38%)from countryside.McNemar test was used to compare the data of ELISA and PCR results with a Qm of 0.037 and a Pr of 0.8474.Conclusions LP might contribute partly to the lower respiratory infections in children less than 5 years.The infection rate of LP increases with age increasing.Urban children have a higher infection rate than those living in countryside.Both methods have a good consistency.