The paper reports a survey made in a focus of muco-cutaneous leishmaniasis in a locality of the lowlands of the State of Rio de Janeiro, Brazil (Baixada Fluminense). The existence of the disease as an endemic of the region was confirmed by the finding of 21 cases with typical scars and responding positively to Montenegro's intradermo-reaction with specific antigen and some of them dating back from 5 to 15 years. At the time of the survey, however, an epidemic outbreak was discovered, coincidig with a great felling of trees for the making of charcoal. Out of 306 persons examined (50% of the local population), 39 presented leishmaniotic lesions (12,7%). Both within the houses and outside, adults Phlebotomus intermedius were captured. From 12 houses, 136 specimens were captured (11,3 per house). Out of 23 dogs examined, one was found with a probable diagnosis of elishmaniasis. Fifteen cats were found negative, as well as 28 small wild mammals. From the 39 patients, 4 had mucous lesions (10,3%), 16 presented multiple lesions (41,0%), and 19 were female (48,7%). There was an absolute predominance of lesions on bare parts of the body. About one third of the cases were children of 10 years or less, confirming the intense domiciliary transmission. Some houses had 2 to 6 patients. On basis of informations furnished by the patients of by their relatives as to the time elapsed since the beginning of the infection, and admitting an incubation period of 2 months, it is possible to conclude that the great majority of infections probably occurred between July and December, coinciding with the great felling of trees already referred to. In 36 cases Montenegro's intradermo-reaction was made, with 2 doubtful and 34 positive results of variable intensity. Eighteen biopsies were made, the epidermis presenting hyperacanthosis, and frquently pseudoepitheliomatosis with corneous globules and micro-abscesses. The dermis showed two characteristic pictures: an infiltration with predominance of plasmocytes or a granulomatous lesion with epithelioid and giant cells. In general, granulomatosis occurred in older cases, isolated or associated to infiltration with plasmocytes. It seems that granulomatosis represents a hyperergic condition of the infected organism, as the patients who showed it had the disease for a longer time and reponded strongly to the intradermo-reaction. Leishmaniae were not numerous in sections. Three patients showed spontaneous cure. Twenty six patients were treated, 16 with tartar emetic, 4 with "fuadin" and 4 with both these drugs. Some of the patients treated with tartar showed toxic symptoms, although the results were as good as those obtained with "fuadin". Two patients with nasal mucous lesions were not cured, notwithstanding the use of both these drugs. Five years after this survey, muco-cutaneous leishmaniasis was absent from the region, probably as a consequence of several preiodical DDT house sprayings to combate malaria during the intervening years (NERY GHIMARÃES & BUSTAMANTE, 1953).