Flows of marsh gas were measured at upland, freshwater marsh, and tidal marsh localities in Delaware in 1971 and 1972, and at a few other localities along the Atlantic coast in the early part of 1973. The gases, mainly methane, were collected in gas-tight flasks, and were analyzed by gas chromatography and mass spectrometry. Other gases detected include principally carbon dioxide, ammonia, ethylene, and hydrogen sulfide. At the localities in Delaware the flows were consistently greater in freshwater and upstream parts of tidal marshes than in the more seaward parts of the marshes where effects of tidal flushing are greater. Increased flows following rainstorms and decreased flows during prolonged dry spells were typical. At scattered localities in North Carolina, Georgia and Florida the higher flows of marsh gas were found in freshwater marshes having moderately negative Eh values, whereas low gas flows were obtained from coastal mangrove and turtle grass environments or from freshwater acidic marshes with weakly negative Eh values. Cultures of a variety of marsh plants and bacterial mud show marked variations in methane evolution according to the species of plant.