Bacteriological, serological, and clinical findings in 128 patients with pneumonia admitted to the medical service of Grady Memorial Hospital, Atlanta, during the 1968-1969 Hong Kong influenza epidemic were compared with the findings in patients with pneumonia admitted during a one-year period beginning July 1, 1967. During the influenza epidemic a threefold increase in the incidence of staphylococcal pneumonia occurred, which accounted for 25.9% of the bacteriologically proved cases. A high correlation between pneumonia, especially staphylococcal pneumonia, and influenza infection was documented. Comparison of preexisting disease in patients with pneumonia during the two time periods failed to reveal any major differences, which suggests similar host susceptibility during epidemic and nonepidemic periods. With no change in the case fatality rate, the excess influenza and pneumonia mortality during the Hong Kong epidemic was primarily due to the increased incidence of bacterial pneumonia.