Crust formation and infiltration rates and their dependence on the exchangeable sodium percentage (ESP) of South African (SA) soils, with kaolinite and illite as the dominant clay minerals, were studied by subjecting them to simulated rain. The final infiltration rate (FIR) values of these soils at ESP ca. 2,5 were compared to values reported for Israeli soils having similar clay content but with smectite as the dominant clay mineral. The SA soils have higher FIR values, which indicates that they were less affected by raindrop impact than the smectitic (Israeli) soils. It is therefore suggested that kaolinitic and illitic soils are less dispersive than smectitic soils. The effect of ESP on infiltration was found also to depend on the clay mineralogy of the soil. The FIR values of the kaolinitic soil with no smectite were only slightly affected by ESP. When smectite was present in kaolinitic soil, the susceptibility of the soil to sodicity, as reflected by crust formation, increased. The illitic soil was found to be more susceptible to sodicity and hence to crusting than any of the kaolinitic soils.