Fast field cycling (FFC) NMR has been relatively little used for solids. This is partly due to instrumental problems and because normal perturbation theory no longer applies when Zeeman fields are of the order of local dipolar fields. Measurements of proton relaxation of solid l-leucinamide over a Larmor frequency range (24 kHz–100 MHz) are described. It is shown that good experimental data can be obtained in the rigid lattice condition and that the results may be explained by modifying conventional perturbation theory to take account of the effects of dipolar relaxation.