Apparatus and procedures for conversion of sample carbon to carbon dioxide, quantitative hydrogenation of carbon dioxide to methane, and radiocarbon assay of the methane are described. Two sizes of counters are used. At the operating pressure of two atmospheres, the larger size contains 0.85 g of carbon and the smaller 0.22 g. If the sample and background are both counted for 24 hours in a 0.85‐g counter, a sample 34 000 years old (26 000 years old in the 0.22‐g counter) gives a C14count equal to twice its standard statistical error. If desired, this method can readily be adapted to larger samples with a consequent increase in the maximum measurable age.