Serum samples are deproteinized with an equal volume of acetone and 20 μl of the filtrate is added to 1 ml of 2.5 × 10−4MKOH and 1.0 × 10−4M 1, 8-dihydroxyanthraquinone in 90% (V/V) acetone. Single point calibration with spiked serum at 1.5 mmol/l is used with unspiked serum as blank. Fluorescence emission is measured at 618 nm, with excitation at 410 nm. Samples analyzed by the described method and by atomic absorption spectrometry showed a correlation coefficient of 0.985. The relative responses for lithium in water, serum eletrolyte matrix and serum were 100, 57, and 44, respectively. The Li response in serum relative to that for Na, K, Ca, and Mg was 480, 600, 33, and 27, respectvely.