In our clinic, we started lithium treatment according to Cooper’s method in 10 consecutive patients with bipolar disorder. In four of these patients, a 24-hour serum level of 0.08 mmol/liter was observed after administering the 600-mg priming dose. According to the nomogram, these patients should have received a dose of 2700 mg/day of lithium. To avoid toxic side effects, we decided to start with a lower dose than suggested by the nomogram. Eventually, doses of lithium between 1200 and 2000 mg/day proved to render adequate serum levels in these patients (0.5–0.8 mmol/liter).