During phototorespiration in C3 plants, glyoxylate is converted to glycine by aminotransferases in the peroxisome. Subsequently the conversion of glycine to serine results in the liberation of ammonia and carbon dioxide in the mitochondria. The enzyme glyoxylate carboligase (gcl; EC 4.1.1.47) catalyses the condensation of two molecules of glyoxylate to form one molecule each of tartronic semialdehyde and carbon dioxide. Transgenic tobacco plants expressing the E. coli gene for gcl (generously supplied by Ying-Yang Chang; Chang et al, 1993, Journal of Biological Chemistry 268 3911-3919) modified by the addition of a peroxisome targeting sequence have been produced. The objective of this experiment was to short circuit the photorespiratory cycle to avoid the release of ammonia and the consequent utilisation of ATP and reduced ferredoxin required for reassimilation. Under low light the T0 transgenic plants appear to grow normally, but under bright light white lesions develop on the leaves. Under photorespiratory conditions, less 14C-glycollate was metabolised to glycine and serine and more to sucrose in the transgenic line than in the wild type plants. Further data on the characterisation of these transgenic plants will be presented.