The present study describes a protocol for the determination of in vivo absolute molar concentrations of Li+ in the human brain using a double tuned 1H/7Li surface coil. The protocol follows the method of Thulborn and Ackerman [J. Mag. Reson. 55, 357–371 (1983)] where the ratio of the signal intensities of 7Li and 1H in the brain is compared to the same ratio in a phantom containing known concentrations of Li+. The 7Li T1 values in the brains of five patients receiving lithium therapy were measured. The average result was T1 = 3.5±0.25s. The phantom solution was adjusted to have this T1 value. The protocol was applied for eight bipolar patients receiving lithium therapy. The average ratio of brain to serum lithium molar concentration was found to be 0.59±0.12.