The aim of this study was to evaluate 4 veneer composites—Signum+EM, Gradia Enamel E3, Sinfony E3, and SR Adoro S1—in a standardized test at 2 different conditions. For each composite, 2 groups of specimens (added to cultures immediately after preparation [ie, fresh] or after 7 days of incubation in cell culture medium) were added to L-929 fibroblast cultures for 72 hours. All composites showed reduced cell numbers compared to glass controls. Fresh specimens of Signum+EM exhibited the least cytotoxicity, followed by Gradia Enamel E3 and Sinfony E3 and then SR Adoro S1. For specimens with 7-day incubation, 3 of the composites (Signum+EM, Sinfony E3, and Gradia Enamel E3) showed similarly low cytotoxicity, while cytotoxic results with SR Adoro S1 were significantly higher. With low in vitro toxicity values in conjunction with good mechanical properties, veneer composites appear to offer an interesting alternative for prosthetic rehabilitation. Int J Prosthodont 2007;20:596–598.