The A. A. show that the available data on the incidence of human plague in Brazil over a long period are not soundly comparable, since only in the recent years it was possible to secure accurate information on the real incidence of the disease. Tabulating in three-year periods the 2610 cases occurred from 1934 to 1945, it may be observed the contrast between the first quarter which includes 47% of the whole incidence, and the remaining periods. A general decrease coincides with the activities of the Federal Government, that in 1936 started a systematic anti-plague program, intensified some years later, with the development of the S. N. P., legally established in 1941. The disease is now limited to the so-called "Brazilian north-east". The state of Pernambuco is the major focus where, since 1934 occured 40 to 50% of the total cases. Studying the cases recorded during the 1941-1945 period, on which better information is available, the A. A. show that out of the 1610 confirmed cases, more than 50% were persons older than 50, 60% were colored people and 51% were male individuals. Excepted 9 cases of pneumonic and 13 cases of septicemic plague, all the patients showed the bubonic form with predominance of inguino-crural localization. The mildness of the disease is clearly demonstrated by its low case fatality rate in the period under consideration: 26%, still reduceable to 12% if exclusion is made of the patients who did not receive any treatment owing to the fact that reporting has been made after death. the case fatality rate shows a rise above the age of 50. It is higher among women and colored people. The admnistration of sulphas in place of antiplague serum reduced the case fatality rate. Studying the different methods employed for laboratory diagnosis, which confirmed about 50% of the positive occurrences, the A. A. analyse the efficiency of "digitotomy" (fingerbone marrow's culture) as compared with viscerotomy, as well as the value of bacteriological examination of blood and material from the buboes. Studying the epidemiological responsibility of domestic rodents the A. A. point out some evidence suggesting that, under certain conditions, Mus musculus may also play an effective part in the spread of the disease. Reference is made to 26 findings of wild rodents naturally infected with plague in the states of Ceará, Pernambuco and Alagôas. Studying the flea indexes regularly determined in 8 cities, the report shows that the number of fleas seems to rise during the rainy season. X. cheopis is the predominant species in the tropical section of the country. Its density decreases as the latitude goes higher, inversely to what happens with X. brasiliensis that is the most prevalent in temperate southern state S. Paulo. Rains and temperature seem to affect differently the two species. Finally, the A. A. analyse the influence of meteorological factors on the prevalence of human plague, showing that in the period on study, the disease predominated in spring and summer. In 4 districts whose meteorological data were available, the infection had its maximum incidence following the periods of heaviest rainfall, under temperature ranges between 19 and 26ºC and relative humidity varying between 66 and 83%.