A laser technique for analysis of carbon-13:carbon-12 ratios with the specificity of laser resonance spectroscopy and the sensitivity and accuracy typical of isotope ratio mass spectrometers is reported. The technique is based on laser optogalvanic effect spectroscopy, in which an electrical (galvanic) signal is detected in response to the optical stimulation of a resonance transition in a gas discharge species. Carbon dioxide molecular gas lasers are used, with the probed transitions being identical to the lasing transitions. Measurements for carbon dioxide samples with 100-second averaging times yield isotopic ratios with a precision of better than 10 parts per million.