As science and technology become more sophisticated and with the rapid computation capabilities of the modern computer available, it becomes both possible and economically feasible to scinetifically study man and his interaction with his working environment. It is now possible for a person seeking employment to expect and obtain a position which will not be unnecessarily hazardous to his immediate health or have detrimental effects over the long run.Manual materials handling is the contributor of over 400,000 back injuries suffered in the U.S. each year. This research is directed at determining the appropriate operator variables to measure for predicting the permissible weight of lift for 3 ranges of lift, floor to knuckle height, knuckle height to shoulder height, and shoulder height to reach height.A modified psychophysical procedure was used during which the subjects were instructed to adjust the weight in a tote box to the maximum wieght they could lift repetitively without excessive strain or fatigue. The lifting exercise consisted of two 20-minute periods. Ninety-five of the 135 used subjects for the experiment were provided by industries and consisted of individuals, both male and female, whose daily activity involved the manual lifting of weights. The remaining subjects were students who were used in floor to knuckle height lifting range.Based on the data obrtained, the lifting capacity of the worker was determined for the different ranges of lift. In addition, predictive models were developed based on the operator variables measured.