Studies have been made on the abrasion by food of different restorative resins in standard Class 1 cavities in mandibular first molars of schoolchildren. The abrasion was recorded by measuring the increasing height of the exposed cavity walls. It was found that Sevriton Simplified was abraded more than Adaptic, that no difference in abrasion between Adaptic and Adaptic without filler could be demonstrated, and that Adaptic was abraded more than an experimental composite containing 30% by weight Aerosil, an ultra-fine SiO2 filler with a grain size of the order of 25-50 nm. The results are in accord with the findings in an initial study by one of the present authors, in which the fillings were placed in denture porcelain teeth. It is stressed that the conclusions of the present work are pertinent only to the type of abrasion studied, i.e. chewing of food without the possibility of direct contact between the fillings involved and the corresponding antagonists.