Six male rabbits were injected on days 0, 6 and 12, subcutaneously, intraperitoneally and subcutaneously with 0.5 ml/kg of a 20% suspension of homologous dental pulp, in complete Freund's adjuvant. Six controls received complete Freund's adjuvant only. Leukocytes were counted regularly. A skin test was performed on day 18. On day 22, a dental test was performed to study the macrophage migration inhibition "in vivo". On day 23, the animals were killed, the teeth and skin were analysed histologically. The following results were observed in the experimental group: 1) inhibition of growth, 2) leukocytosis and eosinophilia, 3) a positive skin test with a strong lymphocytic infiltration, 4) an inhibition of "macrophage migration", 5) pulpal lesions, numbering 1 to 6 per rabbit, with lymphocytic plasmocytic and eosinophilic perivascular infiltration. These results indicate an experimental auto-allergic pulpitis. The mechanisms of human pulpitis ought to be reexamined in the light of these observations.