Detailed biomechanical and psychophysical job evaluations were performed on 55 industrial jobs identified in five major industries (not specified). The medical experiences on these jobs, which comprised 2,934 potentially stressful manual materials handling tasks, were documented retrospectively for 2 years and prospectively for 1 year for 6,912 incumbent workers for a total of over 12.6 million man/hours of exposure. Two biomechanical indices, isometric strength and back compression, and the psychophysical approach, which obtained the individual's own perception of pain or discomfort associated with the task, were used. For both approaches, a Chantillon gauge was used to measure all forces exerted. Three basic categories of overexertion incidents were recognized and recorded during the study: contact incidents (for example, lacerations, abrasions, blisters); musculoskeletal incidents (sprains and strains of muscles and joints, fractures, and joint diseases, but not including the lower back); and back incidents (sprains and strains of the back, degenerative disc disease, and ill defined pain). From the results of this study, the authors conclude that overexertion injuries can be related to physical job stress. Description of the most stressful tasks in a job seems to be more predictive in general than those indices that represent aggregations. The authors view the percentage of the population capable of performing the most stressful aspect of the job (based on either psychophysical strength or isometric strength) as perhaps the best simple index of this type.