The patient--who presented with complaints of fatigue, depression, and disturbed thinking--was referred to a physician trained in environmental medicine. A detailed exposure assessment followed by a red blood cell toxicological metal screen revealed high levels of mercury, likely originating from the patient’s considerable intake of canned tuna. With the onset of depressive symptoms, his tuna intake increased by about 50 percent in response to a nutritionist’s recommendation that omega-3-fatty acids were therapeutic for mood disorders. Subsequent clinical discussion included options for detoxification of accumulated mercury, since mercury is known to accumulate in brain tissue and to act as a neurotoxin. With the avoidance of tuna and interventions to facilitate mercury removal, including use of dimercaptosuccinic acid, the patient’s psychiatric symptoms completely resolved within 8 months; the intrusive ideation disappeared; he discontinued all medication; and returned to work. The author advises that in an era marked by increasing exposure to neurotoxicants such as mercury, health practitioners should consider toxicological factors and use exposure assessment tools with patients who present with mental health complaints and socially disordered behavior. Precautionary avoidance of further exposure and interventions to eliminate toxicants from the body may result in marked improvement or complete recovery. 36 references