An adult male California sea lion (Zalophus californianus) which had been anorexic for 10 days and losing condition, was brought to the University of Tennessee Veterinary Clinic for evaluation. For the past 3 years, the animal had lived in a fresh water pool in an amusement park.  The owners were concerned about a G.I. foreign body since the public could feed the sea lions in this exhibit.  An examination, which included a CBC, serum chemistries, radiographs, rectal culture, fecal, gastric lavage, and a Knott's test for heartworms was performed under general anaesthesia.  The only abnormal findings were a high number of immature neutrophils on the blood count differential and a low serum sodium.  The animal was placed on systemic antibiotics and began to eat a little on the third day of medication.  However, the animal's physical condition continued to deteriorate and 11 days after the original examination, the animal died.  Impression smears of pleural nodules taken at necropsy showed budding yeasts with double contoured walls characteristic of Blastomyces dermatididis.The epidemiology of blastomycosis will be discussed.