The effectiveness of countercurrent immunoelectrophoresis (CIE) used for the accelerated differential diagnosis of pneumococcal, staphylococcal, mycoplasmal and Legionella infections in cases of pneumonia has been shown. The presence of correlation between the results obtained in the bacterial study of sputa and bronchial washings and in CIE has been revealed, which gives grounds for recommending CIE for the accelerated diagnosis of pneumococcal pneumonia on the basis of the analysis of sputa, bronchial washings and blood sera obtained from patients. In Legionella infection the passive hemagglutination test with antigenic diagnostica has proved to be more effective for accelerated diagnosis than CIE.