Influenza was first noted in the north of Chile in the second week of July, 1957 A week later it was present in Santiago and subsequently in the central and southern provinces of the country. It was identified by serologic studies which also showed that the majority of the patients with pneumonia developed antibodies against the A/Japan/ 305/57 influenza virus. The sharp increase of pneumonia in Santiago on Aug. 2 came 10 days after the sharp increase of influenza cases. The twofold increase in deaths during the epidemic was mostly attributable to influenza and pneumonia, and the marked increase in deaths from pneumonia resulted primarily from the increase in total cases rather than from any increase in the proportion of cases that could not be treated successfully. The organism most frequently isolated from fatal cases was Staphylococcus pyogenes. The concerted study of this epidemic gave an early, relatively complete, and valuable picture of the characteristics and potentialities of Asian influenza.