The absorption of 137Cs by sheep following ingestion of contaminated soil was studied using an established dual isotope method. Two agricultural soils were studied: an alluvial gley contaminated by discharges to the sea from the Sellafield Reprocessing Plant, and a lowland organic soil that had been artificially contaminated. Values of the true absorption coefficient of radiocaesium of 0.19 +/- 0.03 and 0.03 +/- 0.01, respectively, were obtained for these soils. This implies that availability of soil-associated radiocaesium for uptake following ingestion is up to about 20% of that when the activity is incorporated in vegetation. These results have been compared to estimates of availability made using an in-vitro approach described previously and found to be in good agreement. However, comparison with in-vitro data obtained for an upland peat indicated that absorption from some upland organic soils could be greater than from the lowland organic soil.