The effect of X-irradiation on <tex-math>$\text{glycine-}1\text{-}{}^{14}{\rm C}$</tex-math> transport in Ehrlich ascites tumor cells was investigated immediately after in vitro radiation exposure in the presence and absence of oxygen, in the presence and absence of bovine serum albumin, and at different cell concentrations. The effect (reduction of transport capability) was more pronounced when the cells were irradiated as a 1:500 suspension than as a 1:10 suspension. There was an oxygen enhancement in both the 1:500 and the 1:10 experiments. Bovine serum albumin exerted a protective influence when present (1:500 cells) during irradiation. Neither the "passive" permeability to glycine (measured at 0°C) nor the fraction of viable cells in the incubation population (measured by aqueous eosin staining) was significantly different from control. Irradiation of the medium prior to addition of cells was without effect within the experimental period. The effect on transport probably involved the indirect action on the plasma membrane, since (1) it was immediate, (2) it was influenced by the volume ratio of cells to irradiation medium, and (3) a nonpenetrating substance afforded protection when it was present during irradiation.

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