The effects of infiltration on sanitary landfill leachate and gas production were examined under both field and laboratory conditions. Maximum field leachate production occurred during spring thaw. Production was greatly reduced during the summer. Moisture absorption prior to leachate flow ranged from 10.0 to 14.2 cm/m of compacted refuse. The leachate produced was strong. As an indication, concentrations of COD, calcium, chloride and ammonia nitrogen exceeded 40,000 mg/L, 2,500 mg/L, 1,200 mg/L, and 600 mg/L, respectively. Decomposition proceeded anaerobically with the production of methane and carbon dioxide. Periods of rapid moisture influx were accompanied by increased leachate strength, reduced pH, and decreased methane production. Modifications to the decomposition environment had interfered with methane production thus allowing the accumulation of organic acids and subsequent reductions in pH. The interference appeared to have arisen from an increase in oxidation-reduction potential.