The anisotropy of solar flare protons (>3 MeV) evaluated at the time of maximum for each of 24 events measured by the University of Chicago experiments on Pioneers 10 and 11 is observed to decrease gradually between 1 and 4.7 a.u. Since diffusive streaming is related directly to the effective diffusion coefficient parallel to the interplanetary spiral magnetic field (K∥), these observations provide a measure of the radial dependence of interplanetary diffusion parameters. An analysis of these results suggests that K∥ increases gradually with r consistent with a radial dependence given by K∥(r) = (8¿3) ¿1021 cm2/sec r0.9¿.4(r in a.u.).