Clinical studies of the effects of rubidium ions on the course of manic-depressive illness are reported. It seems that rubidium tends to increase the length of manic phases and possibly reduces the extremes of mood. Rubidium did not seem to produce any severe side effects in the dose administered, but it has a long biological half-life and caution is still required. Some details of the CSF, RBC, saliva and plasma and urine kinetics are also reported.