This study was undertaken to assess the effect of sound stress on humoral and cellular immune responses to thymus-dependent and independent antigens in mice. After mice were exposed to 4 hr daily sound stessors(83㏈) for 4 days before or after immunization, the primary and / or secondary immune response to sheep red blood cells(SRBC), polyvinylpyrroridone(PVP) or picry1 chloride(TNCB) were assayed. When mice were exposed to sound stressor before or after immunization, delayed-type hypersensitivity reaction and contact sensitivity to TNCB was remarkably depressed compared with those of the unstressed control mice. However, the primary and secondary hemagglutinin response of the stresed mice to SRBC showed a pronounced increase compared with that of the unstressed mice, In contrast to antibody response to SRBC, the primary antibody response of the stressed mic to PVP was almost not detected. surprisingly, the secondary antibody response to PVP of the mice receiving the secondary sound stress was markedly increased when the immune-depressed mice received the secondary immunization with PVP at 46 days after the primary immunization. The susceptibility of mice to intraven-oulsy infected Candida albicans was not changed by the sound stress.