Lifting is one of the major causes of back injury in the workplace. Often, workers are told to ask for the help of another worker when the load is too great to be lifted alone, yet the effects of these team lifts have not been researched until recently. This experiment investigated some of the variables which may affect the results of team lifting tasks. The psychophysical methodology has been used for almost 30 years in trying to determine the maximum acceptable weight of lift for industrial workers. Though two previous studies of team lifting used the psychophysical approach, no effort was made to identify and control variables which may affect team tasks. This experiment manipulated two variables, box type (double or single) and isolation condition (curtains open or closed) to see whether these would produce the psychosocial effects of social loafing and social facilitation. Three male and three female two-person teams performed team lifts, using psychophysical methodology, under all four conditions. The only significant effect found was for gender. Female teams lifted 58.8% of the mass the male teams lifted. Male teams lifted 92.5% and female teams 87.8% of the sum of their individual lifts. This is in close agreement with other studies of team lifting. A regression model was developed in order to predict the amount of weight a team can lift, with an R₂ of 0.962. The external validity of the task conditions was also investigated. / Master of Science