An ordinary and a sustained-release lithium carbonate preparation were administered acutely at equivalent dosage (1.80 g = 24.3 mmol) in a crossover fashion to manic patients. Serum lithium levels were determined by atomic absorption spectroscopy and pharmacokinetic parameters were calculated. Maximum mean serum levels of 1.13 mmol/l and 0.78 mmol/l were achieved at 6 h and 12 h respectively with the ordinary and sustained-release forms. The mean half-lives of absorption, redistribution and elimination were 0.78 h +/- 0.05 (SE), 5.06 h +/- 0.23, 26.8 h +/- 4.5 and 3.73 h +/- 0.37 (SE), 4.42 h +/- 0.28 and 25.6 h +/- 5.5 for the ordinary and sustained-release forms respectively. In healthy volunteers the ordinary preparation was completely absorbed but only 85% of the sustained-release form was absorbed in the manic subjects. Lithium ion distributed into two kinetic compartments and the final compartment appeared to correspond to total body water.