A group of 51 patients treated surgically for ovarian carcinoma was randomly subdivided to test the efficacy of lithium carbonate in the prevention of leucopenia during systemic chemotherapy. In 26 patients receiving sequential lithium carbonate the side effect of myelosuppression was mitigated and the leucocyte count during treatment, which determines the dosage of the cytostatic drugs, was significantly higher in this group. It was, thus, possible to reduce the number of cytostatic courses of treatment in the lithium group in comparison with the treatment courses in the 25 control patients. Lithium therapy had to be discontinued due to side effects in seven patients, which were then excluded from the trial.