Uninfected plantlets of Goodyera repens and plantlets infected with the endophyte Rhizoctonia goodyerae-repentis were fed with 14CO2. Quantities of 14C fixed varied greatly between individuals, but there was a consistent pattern of distribution of label which remained unaltered over four weeks. Very little 14C moved to the rhizomes. The endophytic fungus readily grew from infected plantlets on to Pfeffer agar and small amounts of radioactivity were found in the mycelium growing from previously fed plantlets. 14C leakage from uninfected plantlets was negligible, although low levels of radioactivity occurred in serial washings from them. When the tops alone of infected plants were fed with 14CO2, no radioactivity could be detected in the emerging fungal mycelium. Where rhizomes alone were exposed, small quantities of 14C were detected in the growing mycelium. The fungus readily translocated 14C from the remains of dead protocorms. It appears that R. goodyerae-repentis does not freely utilize recent photosynthate from its host under the conditions of these experiments.