The number of organizations re-examining their manufacturing strategies in the automotive parts supply industry in North America is increasing. Competitive pressure, both foreign and domestic, is fuelling the need for change. Customer emphasis on quality further acts as a stimulus to strive for perfection within an organization. One method to which manufacturers have been turning in order to improve their competitiveness is the implementation of the Japanese management technology called Just-in-Time (JIT). The purpose of this paper is to provide a statistical analysis of any cost function differences that exist between groups of auto parts manufacturing firms that have adopted the JIT philosophy and those that have not. The significance of differences in input use and substitutability is explored using a generalized CES-translog model. Primary empirical findings of this research lend support to the conclusion that JIT firms do appear to be distinct from the non-JIT group. In many cases, the elasticities of factor substitution calculated from the two groups of firms are significantly different. Additionally, the difference between the elasticities of factor productivity, with respect to output changes, tends to show the JIT firms as being more factor saving than the non-JIT firms.