We have analyzed the properties of ~30 to 130-keV/e protons and alpha particle upstream of six quasi-parallel interplanetary shocks that passed by the ISEE 3 spacecraft during 1978--1979. Our measurements were performed with the University of Maryland/Max Planck Institute ULECA sensor. We deduced the energetic particle diffusion coefficients, &kgr;∥, by calculating the difference between the bulk flow speed of the particles and their estimated scattering center speeds in the spacecraft frame and relating this to the particle spatial intensity gradients upstream. This calculation yielded diffusion coefficients for each 2-min interval in the last ~15 min before shock passage, when the particle intensities were high. Comparing these diffusion coefficients in detail with the theory of Lee (1983), we find that upstream of the shock the A/Q dependence of &kgr;∥ for alphas and protons agrees well with the theory. Upstream of the shock, &kgr;∥ often increases with distance, as predicted by Lee's theory, although the details of this increase do not agree with the theory. At the shock front itself we find excellent agreement between theory and observation for (1) the velocity dependence of &kgr;∥, and, (2) the dependence of &kgr;∥ on the magnitude of the proton distribution function. ¿ American Geophysical Union 1989