Recent measurements of the carbon isotopic abundance of atmospheric methane give a value of Δ(13C/12C)=-47.0¿0.3%0, which is significantly different from earlier values measured by others between 1950 and 1970. The isotopic composition of various sources and the possibility of a temporal trend are discussed. The average methane concentration measured was 1.66 ppm, which is in accord with the increase in concentration since 1965--1970 observed in other studies.