Over 600 sera of patients with clinical diagnosis of M. pneumoniae infection were examined using complement fixation (CF) test; 91 gave positive reactions and were selected for a comparative analysis with other methods such as metabolic inhibition (MI), mycoplasmocidal (MC) and radioimmunoprecipitation (RIP) methods. MC and RIP test gave antibody titers comparatively higher than MI and CF. Comparative studies on the sensitivity of these methods were also carried out on 6 paired sera collected from the same patients at 10 day intervals. The increase in antibody titers were much higher when MC and RIP tests were considered. When RIP and MC methods were compared, RIP appeared more sensitive in all cases.