Tissue regeneration after therapeutic manipulations is essential in periodontology, ral surgery, and trauma of the periodontal tissues. Local inflammation because of oor oral hygiene also plays a crucial role in the above situations. Local inflammatory reaction, accompanied by the local production of cytokines, profoundly influences bone turnover and regeneration. Several products of low immunogenicity for augmenting tissue regeneration have been recently proposed as boosters of soft and mineralized tissue regeneration. Among them, Emdogain, an amelogenin derivative of porcine origin, has recently been introduced. Clinical results indicate that this product might be a good additive, producing fast tissue regeneration with no apparent clinical side effects. In contrast, very little is known about its in vivo immunologic effects. A previous study showed that Emdogain does not modify the cellular or humoral immune response in vitro. In the present work, performed in 10 patients, only a slight, nonsignificant activation of the immune system occurred during the first year following Emdogain application. Neither cellular immunity nor humoral immune response was significantly modified. In addition, the in vitro response of the patients' lymphocytes to Emdogain was assayed 2 and 12 months postoperative. We did not find any significant specific lymphocyte transformation in the presence of Emdogain, although lymphocytes could be stimulated by nonselective mitogens. These results indicate the immunologic safety of the agent in vivo, at least after 1 year.