The concentration of methane has been measured in tropospheric air samples collected in remote locations between 55 ¿N and 53 ¿S during six collection periods between November 1977 and November 1980. The observed concentrations of CH4 have increased in each of six latitude locations by an average of 0.052¿0.005 ppmv between January 1978 and 1980. This (1.4¿0.2)¿1014 gram increase in the total atmospheric burden of CH4 corresponds to 35¿12% of the yearly flux of (4.0¿1.3)¿1014 grams needed to maintain the CH4 concentration in steady-state at its recent level of about 1.6 ppmv. The 1978--1980 excess of about 0.7¿1014 grams per year of sources over sinks for CH4 could arise from either an increase in biogenic releases or from a decrease in the average OH radical concentration in the lower troposphere, or from both.