The development of an instrument to measure load, power, and margin in life (MIL) is described. Validity was established through factor analysis and the known-groups approach to construct validity. Stability was tested through a testretest reliability, and Cronbach alpha reliability coefficients were obtained to test for internal consistency. Subjects consisted of 146 adult men and women volunteers for testing Form 1, later revised to Form 2. Form 2 was given to 103 volunteers; of these 66 were repeaters from the Form 1 testing; 37 were new subjects. Item analyses were performed and used to reduce the original 211 items to 94 for Form 3 of the scale.