A group of male Wistar rats (strain AF/HAN) received carrageenin in a tragacanth suspension and saline solution by subplantar injection into the right and left hind paws, respectively. Another group was treated similarly with Mycobacterium butyricum in Freund's adjuvant given in the right hind paw while the left paw served as control. The experiments ran for 20 days. The paw volume was measured plethysmometrically and general histological examination was carried out on samples of the dorsal paw epidermis and dermis. The mast cell count and thickness of epidermis were also determined. Epidermal and dermal changes developed in distinct stages following carrageenin or adjuvant treatment. During the acute phase (from 0 to 12 h post-treatment) the paw volume as well as the thickness of the epidermis increased while the dermal mast cell count decreased. Furthermore, hyperemia, edema and leukocytic infiltration of the connective tissue was observed. Eosinophilia and focal necrosis appeared only in the adjuvant treated animals. In the subacute phase (from 1 to 3 days post-treatment) paw swelling and epidermal hyperplasia recessed slightly in the carrageenin treated group. On the other hand, paw volume of the adjuvant treated animals continued to rise. These changes were accompanied by proliferative and degenerative processes of the connective tissue (fibroplasia, histiolymphocytic infiltration, focal necrosis). A chronic phase of inflammation (from 4 to 20 days post-treatment) developed only in the adjuvant treated group. Epidermal hyperplasia reappeared and the paw volume increased significantly (secondary reaction). Also granulomatous chronic inflammation and foreign-body giant cells proliferated in the connective tissue.