Young standard dark mink developed classical symptoms of biotin deficiency, including underfur-greying, "spectacle eye," loss of fur, exudates from eyes, nose and mouth and encrustation of paws, when fed a diet containing 10% commercially produced, denatured spray-dried eggs. Comparable animals fed 5% spray-dried eggs did not show these symptoms; however, their pelts tended to be browner (i.e., lighter colored), than those of control animals. The feeding period during which these symptoms developed covered about 4 1/2 months: August 1 to December 13. Supplemental biotin (1.34 and .45 mg d-biotin per kilogram dry feed) prevented deficiency symptoms in mink fed 10% spray-dried egg of 20% fresh frozen whole chicken eggs, respectively. Eye exudates were most severe in October, when the combined stress of body and fur growth was greatest, then showed a partial remission as peak growth of body tissue and fur was passed. It was concluded that spray-dried eggs are insufficiently heat-treated to render their avidin content inactive; thus they should be appropriately supplemented with biotin for use in mink diets.