1. A series of 19 different samples of flies collected within epidemic areas during and after the onset of nearby human cases of poliomyelitis have been tested for the virus of poliomyelitis. Four of these samples proved positive.
2. Methods used in collecting the flies, preparing the inocula, and examining the inoculated monkeys (and other animals) are described.
3. All of the positive tests were obtained by the intranasal and intra-abdominal inoculation of Java (cynomolgus) monkeys. Green African and rhesus monkeys represented the smaller number of other monkeys used in which only negative results were obtained.
4. All of the positive samples (as well as nearly all the negative ones) contained "blow flies," and green bottle flies.