Many studies have reported that stress affects the immune system. It is known that professional drivers are exposed to various forms of job-related stress. The aim of the present study was to investigate the job stress of taxi drivers based on the mitogen responses and cytokine production of peripheral blood lymphocytes (PBMC), combined with interviews on lifestyles and income. We examined randomly selected male taxi drivers aged 40-59 years who were members of the Kansai District Union of Private Railway, Hire, and Taxi at the end of 1992 and 1993. At the end of 1993, they were struck by a severe economic depression. The lymphocyte proliferative responses to phytohemagglutinin (PHA), concanavalin A (ConA), poke weed mitogen (PWM), and PHA-induced interleukin-2 (IL-2) and IL-4 production of the taxi drivers were at the same level as those of the control subjects as measured in 1992.The mitogen responses and IL-2 production of taxi drivers were found to have significantly decreased in 1993, while their IL-4 production was significantly elevated. Lifestyles of normal PHA respondents were significantly different from those of low-PHA respondents in 1992. However, in 1993, these differences were unclear. The immune alterations of taxi drivers who were prohibited from working overtime were more profound than those of the drivers who were allowed to do so. These results indicate that in addition to driving stress, the daily earnings affect taxi drivers as a strong stress or that induces immunological changes.