One of the primary reasons that the control of photorespiration has attracted attention as a possible means of improving plant productivity is that it is possible to artificially reduce photorespiration and oxygen-inhibition of photosynthesis in experimental situations which permit an assessment of the effects on growth and yield. Photorespiration was originally observed as a transient burst of CO2 evolution which occurred immediately after leaves were darkened. Photosynthesis is diminished by concurrent photorespiration, and photorespiration is obscured by photosynthesis. For this reason, methods of assessing photorespiration commonly employ artificial conditions which suppress photosynthesis, or indirect measures which assess the influence of photorespiratory activity on photosynthesis. Glyoxylate, the product of the glycolate oxidase reaction, is a very reactive compound and may undergo a variety of theoretically possible metabolic fates. The degree to which these alternate possibilities are realized in vivo may exert a strong effect on the stoichiometry of photorespiration.