It had been postulated that the increased film area of a charged overbore tube would be counterbalanced by the lower temperature fuel surface and decreased flux so that the radioisotope content of the effluent would be the same as that from a normal tube. In order to confirm or deny the postulate, Tube 3267-C was equipped with an effluent sample line under the provisions of PT-IP-543-A. Sampling and analytical work began in mid-April and continued through November, 1963. Effluent samples obtained from an overbore tube at C Reactor over a nine-month period were analyzed for P{sup 32}, As{sup 76} Np{sup 239} and Cr{sup 51}. Based on the results obtained for these isotopes, it can be concluded that the radioisotope content of the effluent from an overbore tube will be the same as the radioisotope content of the effluent from a normal size tube operating under similar conditions.