[en] Recent theories have related the diffusion of cosmic rays in the solar wind to the power spectrum of interplanetary magnetic field fluctuations. In this study the power spectrum-diffusion coefficient relation for low-energy protons (T<80 MeV) is tested directly, and the relative contribution to the scattering from directional discontinuities in the magnetic field is examined. Modulation parameters V/subw//K/sub rr/, the solar wind speed divided by the radial diffusion coefficient, are calculated from Pioneer 6 magnetic field and solar wind data are compared with simultaneous Imp 3 observations of the 20- to 80-MeV proton flux. Daily variations in the 40- to 80-MeV proton flux are found to respond to changes in V/subw//K/subrr/ as is predicted by a perturbation solution of the Fokker-Planck equation once the contribution from directional discontinuities in the magnetic field is subtracted from the diffusion coefficients. This finding is interpreted to imply that a large percentage of the identified discontinuities are basically tangential. A lack of correlation between the 20- to 40-MeV flux and the parameter changes is interpreted as being due to either the invalidity of the theory at lower energies or the presence of a continuous flux of high-energy solar protons. A well-defined time lag between changes in the 60- to 80-MeV proton flux and corresponding changes in V/subw//K/subrr/ is observed during a period when the interplanetary magnetic field is predominantly radial and the Imp 3-sun-Poineer 6 angle is greater than 10degree. This lag is consistent with the interpretation of little or no cross-field diffusion or a perpendicular diffusion coefficient less than 3times10¹⁹ cm²/s