A 66-year old female on long-term lithium therapy, developed neurologic toxicity with coma and convulsions. The treatment consisted artificial ventilation, fluid and electrolyte infusions and a six hour hemodialysis (HD) on days 2, 3 and 4. The convulsions disappeared on day 4; the patient regained consciousness on day l2 and recovered with slight sequelae. Toxicokinetic studies were conducted for a period of 12 days. The lithium (Li) serum concentration fell from 4.4 mmol/l on admission to 2.16 before HD and 0.35 after three HD. Li serum half life was 54 hours before HD, 25 hours during the three days on which HD was carried out and 106 hours thereafter. The Li cerebrospinal fluid/Li serum ratio ranged between 0.4 and 0.6 and was not influenced by HD. Mean renal clearance was 10.6 ml per min. During hemodialysis, Li serum half life decreased to 3.5 - 4.9 hours and clearance was 108 ml/min. A total amount of l28.6 mmol lithium was excreted; 84.3 mmol by HD and 44.3 mmol in urine. Patient's clinical course and electroencephalographic signs were correlated with the calculated cellular pool of Li but not with Li serum concentrations. This study confirms the effectiveness of HD to decrease the cellular pool of lithium. However, rather than considering only the absolute Li serum concentration, the presence of a rebound peak after HD may be viewed as indication for further hemodialysis.