The accident at the Chernobyl nuclear power plant in 1986 resulted in levels of radiocaesium in animal-derived food products above national intervention limits in a number of countries. In upland areas of the United Kingdom (UK) radiocaesium activity concentrations in the meat of some sheep exceeds (in 1998) the local intervention limit of 1000 Bq kg(-1) and measures are still in place to restrict the entry of such animals into the human food chain. The use of many established countermeasure techniques is difficult due to the nature of animal management in the affected areas. This paper describes a study to develop and test a bolus containing the radiocaesium binder ammonium ferric hexacyanoferrate (AFCF) suitable for administration to small lambs of hill-sheep breeds used in the UK. It was found that a bolus 14 mm x 50 mm in size, and containing 20% AFCF, could be safely administered to lambs of 10 kg. An increase in the AFCF content above 20% resulted in too rapid a breakdown of the bolus. Administration of three boli per lamb reduced the Cs-137 activity concentration in muscle by circa 50% between 3 and 8 weeks following administration of the boli. After 12 weeks the reduction in the Cs-137 activity concentration was 30%. We conclude that the AFCF bolus developed could be effectively used to reduce the radiocaesium activity concentration in lambs within hill and upland areas of the UK.