An epizootic disease in pigeons associated with atypical pneumonia in two persons handling the birds has been studied. Most of the observations made during the work were consistent with the idea that we were dealing with an infection caused by a member of the psittacosis-lymphogranuloma venereum group of viruses. The outbreak was peculiar, however, in that tissues of the diseased pigeons contained many intranuclear inclusions and that the viruses isolated from these birds produced both intranuclear inclusions and elementary bodies in the cytoplasm of cells of chorio-allantoic membranes of the developing egg. Whether the pigeons were simultaneously infected with two viruses or whether the virus of pigeon psittacosis can produce intranuclear inclusions under certain conditions remains to be determined.