Microorganisms were found in about 300 Mallophaga ( Menopon gallinae, Eomenacanthus stramineus , Goniocotes gallinae) and 11 host hens. The majority of isolated bacteria was determined as grampositive cocci. The microflora found on the surface of and inside the Mallophaga as well as in the samples of hen's skin did not exhibit significant qualitative differences. The internal microflora in Mallophaga appeared qualitatively a little poorer than the external. Breeding of bacteria from interior tissues of nymphs of G. gallinae seldom succeeded, although bacteria were found in all microscopical preparations. The results indicate the bacteriostatical effect of an unknown agent in the digestive system of Mallophaga, as well as the presence of microorganisms (probably specific to the insects investigated) which, however, cannot be distinguished by the usual methods.