AbstractA series of over 400 well‐documented biopsies of mucocutaneous leishmaniasis was evaluated to elucidate the histological processes associated with the elimination of parasites, and their correlation with the course of the disease. Non‐specific inflammation was the most frequent and least effective response; its onset might be delayed, and in this event particularly the incidence of metastasis from skin to mucosa was high. Lysis of parasite‐laden macrophages appeared to be the basic mechanism of parasite reduction, even when it was not overt. When it was acute the onset was usually rapid, and though it resulted in much tissue destruction the prognosis was generally better and mucosal metastasis rare. Lysis and non‐specific inflammation both led to the formation of a post‐necrotic type of granuloma, but reversion of the process was almost as common as progression. Ultimately a tuberculoid granuloma evolved and proceeded to resolution. In about 5 per cent of cases, macrophage activation appeared to bring about early resolution; neither reversion nor mucosal metastasis was seen.