Seasonal fluctuations of Diptera indigenous to domestic solid waste were examined at the Gainesville, Florida, municipal compost plant during 1968–1969. Populations of both immature and mature forms were estimated and the efficiency of chemical and physical control procedures was tested.The major fly source at the compost plant was larvae-infested incoming refuse.Phaenicia cuprina(Shannon) comprised more than 97% of these larvae which migrated into protected areas where they developed into adults producing approximately 450,000 adult flies per week from June through September. This population could be reduced by 63.5–80.7 percent by procedural changes and good housekeeping.Daily application of a dichlorvos sugar bait reduced the number of flies by 66.7– and one application of dimethoate to the night-time roosting sites reduced the population by 97.5– for 1 week.Recommendations for fly control at refuse processing plants are listed.