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In an attempt to obtain information on the aetiology and histogenesis of granulomatous nodules as described in wild or cultured fishes, rainbow trout, Salmo gairdneri Richardson, and turbot, Scophthalmus maximus (L.), received subcutaneous and intraperitoneal injections of talc and BCG. The development of dermal, perivisceral, peritoneal and gill nodules occurred after 15 days, and the evolution of early solid, then mature necrotic (BCG) or cystic (talc) nodules followed until the ninetieth day. The presence of the injected material was demonstrated within phagocytic epithelioid or giant cells. Turbot responded more intensely to experimental injection than rainbow trout. Histological descriptions allowed a distinction between neopiastic nodules, epithelial liver pseudo-nodules, histiocytie nodules (melanin-macrophage centres), and reactional granulomatous nodules. In the last case, the specific structure and development may correspond to different causes, some well known (infection, foreign bodies), others enigmatic and possibly related to immunological reactions.