The concentrations of zinc in serum, leucocytes and hair of normal dogs, dogs with zinc-responsive dermatosis and dogs with dermatitis not associated with zinc deficiency was determined. The mean concentration of zinc in serum and hair of dogs with zinc-responsive dermatosis was significantly lower than in other dogs but the range of zinc concentrations overlapped that of the other dogs. The mean leucocyte zinc concentration was similar for each group of dogs. It is concluded that low zinc concentrations in serum and hair have only a corroborative value in the diagnosis of zinc-responsive dermatosis in dogs.