This Data Item presents a method for calculating values of compressive contact stress in the contact region between a disc cam and a domed or flat-faced follower at regular intervals during one rotation of the cam. The calculation of contact stress is a vital step in the design of a cam mechanisms and is specially useful when selecting a suitable material and heat treatment for the cam surface. The method involves calculation of the force acting at the cam/follower interface due to follower system inertia@ to externally-applied load and to the action of the return spring. Values of contact force@ together with values of cam profile curvature@ follower dimensions and the materials properties of the cam and the follower@ are used to calculate contact stress. A Fortran computer program (ESDUpac A9411) that performs all the necessary calculations is provided with this Data Item. Also provided is a Windows executable interface program (VIEWpac W9411) that contains the Fortran code and allows the program to be run in a user friendly manner. The programs include an option allowing the user to determine suitable values of spring rate and preload to ensure that contact between the cam and the follower is maintained. The Item includes a full description of the mathematical model on which the calculation is based together with guidance on the use of the program@ including interpretation of the output. Three examples illustrating the use of the program are presented.