1 The serum lithium concentration was measured before dosing, and at 2, 4, 6, 8, 10, 20, 22, and 24 h after three proprietary preparations of lithium carbonate (Camcolit, Phasal or Priadel). 2 A total of twenty-eight studies were performed on eleven patients. In seven studies the patients received Camcolit, in ten studies patients received Priadel and in eleven the patients took Phasal. 3 The dose of each preparation was adjusted during a 10 week run-in period to maintain the serum lithium within the normal therapeutic range (0.6-1.2 mmol/1). Five patients received one lithium preparation, one patient received three lithium preparations and five patients received four lithium preparations consecutively. 4 After a single daily dose of Phasal and Priadel, the serum lithium remained within the therapeutic range for 24 h. 5 After a single daily dose of Camcolit, the serum lithium remained within the therapeutic range for only 12 h. 6 After three doses of Camcolit (given at 0.800 h, 12.00 h, and 18.00 h) each day, the serum lithium was maintained in the therapeutic range for 24 h.