Blood constituents were measured in salmon (Oncorhynchus gorbuschaandO.nerka) at various times during the spawning migration. Values for blood sodium, potassium, calcium, glucose, protein, and hematocrit suggested that during early stages of migration through post-spawning these fish experience a syndrome reminiscent of mammalian hypoadrenocorticism. The reverse was true of fish in advanced stages of senescence. Older fish also suffered ascorbate deficiency with a resultant necrosis of the skin. This deficiency was corrected by intraperitoneal injection of ascorbate. Various forms of hormone therapy applied to senescent fish were unsuccessful in prolonging their life appreciably.