The occurrence and relationship of various complaints in lambs and hoggets, preventable by selenium prophylaxis, are reviewed. The excretion and tissue retention of selenium by animals on normal feeds and on oral dosing with sodium selenite are given. Faecal excretion of selenium, even on low levels of intake, is high and it is suggested that reduction of dietary selenium to a non-available form occurs in the rumen. In all animals investigated, the kidney showed the highest selenium levels and was the organ most influenced by selenium absorption. The kidney selenium levels provide an adequate index of the animal's selenium status. Tissue selenium levels from healthy, white muscle, and ill-thrifty lambs and hoggets were investigated. There is evidence that the occurrence of muscular dystrophy in lambs, but not necessarily in hoggets, is related to lowered tissue levels of selenium. Findings with respect to ill-thrift and selenium tissue levels were equivocal. The above work is considered together with published information on the nutritional causes of muscular dystrophy in sheep.