Biological screening of dental materials which are intended for use in contact with the oral mucosa comprises a mucous membrane irritation test. The aim of the present investigation was to study the effect of 3 periodontal dressings on intact oral mucosa and to assess their effect on the epithelial proliferation during wound healing. A total of 87 rats were used, 24 for studying reactions in intact mucosa and 63 for a wound healing study. A wound was inflicted on each animal in the palate behind the incisors. The dressing covered the wound area and the surrounding mucosa and was secured by an appliance fixed to the maxillary incisors. 3H-labelled thymidine was injected prior to sacrifice after observation periods of 1, 3 and 5 days. Histological assessment and autoradiographic evaluation of mitotic activity were performed. The dressings caused no reaction in the intact mucosa. In the wound healing study the mitotic activity at day 1 was lower in test than in control animals indicating a toxic effect of all materials. No differences between the 3 dressings were found. After 5 days, all wounds were covered by epithelium. Neither at 3 nor at 5 days were any differences between test and control animals seen.