Culicoides peleliouensis was very annoying to personnel of the U. S. Armed Forces on Peleliu and other islands of the group. The gnat breeds primarily in decomposing organic material on the margins of brackish tidal swamps. Its abundance is periodic, corresponding to the 2 periods of low tides during the month. The gnat may fly as far as 2 miles in a light breeze. It is attracted to clear, intense light. Specimens have been taken from airplanes arriving at Saipan from Peleliu. Best control was secured by dusting breeding sites with a 10% DDT dust 3-5 days before anticipated high population periods. DDT-xylene-Triton emulsion can also be used. Removal of marginal swamp vegetation is desirable. Diesel oil alone or with 5% DDT was not effective.