Although many workers suffer from chronic hepatitis, the influence of labor on its clinical course is not clear. We prospectively followed 89 workers with chronic hepatitis for 3 years, and examined the relationship between job-related factors, such as job class, job type, working hours and work effort, and the liver function test. There were no job-related factors that had any influence on the activity of hepatitis. Moreover, no significant relationship was found between job-related factors, including tiredness, and the acute exacerbation of hepatitis. No significant changes of aminotransferase levels and of platelet counts divided by each job-related factor were found during the observation period, but the platelet counts decreased in workers with acute exacerbation, but without clinical significance. These results suggest that job-related factors have little influence on the clinical course of chronic hepatitis during a relatively short observation period.