The in vitro occlusal wear of two recently introduced, small-particle composite resins was evaluated. Twelve disks of each material were opposed by maxillary third molars and subjected to 300,000 masticatory cycles in a servohydraulic model of the human masticatory apparatus. Before and after profiles of the surfaces of both the disks and the teeth were mapped and digitally recorded on magnetic disks. P-50 disks showed significantly (P .05) less volume loss than did Herculite disks. Enamel that opposed P-50 disks showed significantly (P .001) more near than did enamel that opposed Herculite disks.