A study is presented of the relationship existing between simultaneous fasting spinal fluid sugar and blood sugar. A definite correlation between the blood sugar and spinal fluid sugar is indicated. In a group of 46 control patients the mean percental relationship was found to be 62 with a standard deviation of 7.In schizophrenia no deviation from the control series was encountered. In manic depressive psychosis the mean percental value for the entire group was within the normal range but there were marked individual variations particularly in patients in the manic phase. In general paresis, admission specimens showed low mean percental values, which tended to approximate the control series following treatment.