It has been suggested that neutrons produced by cosmic radiation should form radiocarbon by the reaction N14(n,p)C14 in such amis, that all C in living matter should be radioactive to the extent of 1-10 disintegrations/min./g. In view of the 5,000-yr. half-life of radiocarbon, it was further expected that it should be absent from such old C sources as petroleum, coal, or limestone. These predictions were investigated by examining the radioactivity of 2 series of isotopically enriched samples of methane. The first was derived from petroleum methane (petromethane) and the other from methane from the Patapsco Sewage Plant of Baltimore (and referred to as biomethane). Measurements on enriched biomethane established the activity of "living" C to be 10.5 disintegrations/min./g., in good agreement with the predicted value. However, enrichment of petromethane by a factor of 25 failed to show activity beyond the limits of exptl. error, in line with the theory that cosmic rays produce the activity. The discovery of cosmic-ray C has interesting implications in the biologic, geologic, and meteorologic fields.