In 15 lithium-treated psychotic patients, the following variables were examined over two years at 6-monthly intervals; seru lithium levels, serum electrolytes, thyroid function, urinary creatinine and urea, and clinical EEG. The mean serum lithium level was 0.64 mval/l and did not change during the two years. When compared to the pretreatment EEG, visual analysis did not indicate any specific potentials, focal signs, or asymmetrical phenomena such as have been reported in the literature. Only at the beginning of treatment could a small increase in unspecific, abnormal changes be demonstrated, which, however, decreased during the following 18-month period of investigation.