The effect of improved work conditions on symptoms of mental strain was examined in a longitudinal study of metal industry employees. The aim was to study the changes in work conditions, job satisfaction, and indices of mental strain among the employees who were promoted or who changed employer in comparison to those who had stayed in the same job during the five-year follow-up period (matched groups, N 136). During the study period, work content and physical work environment had significantly improved in the job-change group compared to the reference group. Job dissatisfaction, life dissatisfaction, and stress symptoms had decreased significantly in the job-change group. The most powerful predictors of changes in job stress or general mental strain were changes in work content and changes in the quality of the physical work environment. However, the multiple correlations obtained in the regression analyses were not high.