THE LITERATURE abounds in references to cases of empyema with particular emphasis on technics of treatment. Burpee1 reviewed a series of 500 cases in 1936, while Hochberg and Kramer2 reported on 300 cases and Lanman and Heyl3 analyzed a large series, both in 1939. Shanks,4 in 1944, compiled an excellent review of the literature and an analysis of 169 cases in Dayton, Ohio, since 1927. Most authors are in agreement that pneumococci account for 75 to 80 per cent of all cases of empyema, with streptococci and staphylococci etiologically involved in all other cases except for approximately 1 per cent, in which rare pleural invaders, such as Escherichia coli, Brucella abortis, Ascaris lumbricoides and Hemophilus influenzae, are implicated. The object of this paper is to present in detail the history, hospital course and subsequent follow-up observations in a case of empyema caused by H. influenzae in