The effect of compression ratio on the following mechanical properties of cheeses was studied: compression force, work ratio, adhesive force, recovered height, and compression ratio at the inflection point. The mechanical properties changed with compression ratio in a unique pattern for each type of cheese; changes in work ratio and recovered height produced the most distinctive patterns. The mechanical responses of imitation processed American cheese to changes in the compression ratio clearly differed from those of natural ripened cheeses. The correlations between sensory evaluations of hardness, chewiness, springiness, and adhesiveness, and the mechanical properties measured by instrument changed with the compression ratio used for the instrumental determinations. Therefore, the optimum compression ratio to be used for instrumental determmations of mechanical properties must be evaluated for each property with the fitness test correlating instrumental and sensory evaluations. Copyright © 1979, Wiley Blackwell. All rights reserved