Sendai viral infection enhances mice lung response to Saccharopolyspora rectivirgula (SR). The mechanisms of this viral enhancement remain unclear. The present study was done to verify if the viral infection was required and if the presence of the viral infection needed to be given simultaneously with the SR antigen for the enhanced response to occur. In a first experiment groups of C57BL/6 mice were instilled concomitantly with SR and live or inactivated Sendai virus. In a second experiment the viral infection in the appropriate group preceded the SR challenges by 4 weeks. As reported previously SR induced a cellular inflammatory response. This effect of SR was enhanced by the viral infection but not by inactivated virus particles. Total lavage cells 3 weeks after the virus inoculation in the appropriate groups were: saline = 69 +/- 15 x 10(3); SR = 678 +/- 104 x 10(3); Sendai = 277 +/- 61 x 10(3); inactivated Sendai = 73 +/- 23 x 10(3); SR + Sendai = 1232 +/- 232 x 10(3); SR + inactivated Sendai = 515 +/- 54 x 10(3). In the second experiment, where the infection preceded the SR challenge, no enhancement was observed. We conclude that Sendai virus enhances mice lung response to SR by an infectious process when both SR and the virus are present simultaneously.