Red blood cells from 18 lithium carbonate-treated patients with bipolar affective disorder and 12 normal volunteers were analyzed using 1H-nuclear magnetic resonance (NMR) spectroscopy. The spectra were analyzed for alanine, adenosine triphosphate (ATP), choline, 2,3-diphosphoglycerol, glucose, glutathione, glycine, and lactate. Significant elevations of choline and lactate were found in the lithium-treated patients compared with normal, unmedicated subjects. The elevation of lactate due to anaerobic metabolism in the red blood cells was further investigated via fluorometric analysis and appears to be caused by blood standing at room temperature. The observed increases in red blood cell choline are sufficiently high and statistically significant to warrant additional studies on the dramatic effects of lithium on this red cell metabolite, which might be important for an understanding of its mechanism of action in psychiatric disorders.