A colony of thirteen male and female deer have been studied for seasonal fluctuation of blood calcium phosphorus, albumin, globulin, and alkaline phosphatase. The female animals had stable levels of these parameters of body chemistry throughout all periods of the years. The male animals, beginning in May, undergo rapid antler growth, producing a structure equivalent to one-sixth the total skeletal bulk in a three-to-four-month period and have stable levels of calcium, phosphorus, albumin and globulin. This group demonstrated marked rise in serum alkaline phosphatase activity directly coordinated with the rate of antler growth. Amputation of the antler formation led to a sharp decline of circulating alkaline phosphatase, indicating this structure is the source of the enzyme.