In a laboratory and greenhouse investigation into the uptake of Cs-137 by oats and alfalfa, both the concentration and uptake of Cs-137 were found to vary widely for a number of Canadian soils. The Cs-137 concentration in oats were found to be related to the degree of fixation of Cs-137 by the soil and to the available K content of the soil in that plants grown on soils with high fixation of Cs-137 and high available K content were low in Cs-137, whereas plants grown on soils with low fixation of Cs-137 and low available K had a higher content of Cs-137. Although it was considered possible that plants could utilize non-exchangeable Cs-137, results obtained by an experiment using alfalfa as a test crop failed to prove this possibility. The time of application of CaCO3 or K relative to the time of application of Cs-137 was found to influence the uptake of Cs-137 by oats. When CaCO3was applied 1 month prior to the application of Cs-137, the uptake of Cs-137 was less than when the Cs-137 was applied 1 month prior to the CaCO3. The reverse trend was found for K. Cesium-137 taken up by alfalfa increased with each cutting over a period of four cuttings for four soils, but not for two acid soils.