Estimation of the total body vitamin B12 in the live subject.

1. Values for total body vitamin B,, were calculated for eighteen patients by giving a tracer dose of radioactive cyanocobalamin and measuring the radioactivity and microbiological activity in liver biopsies obtained at laparotomy. 2. The values for total body vitamin B,, ranged from 960 to 5984pg with a mean of 2528 pg. Five values were greater and thirteen less than the mean. 3. Significant correlations were found between the serum vitamin B,, and total body vitamin B,,, the serum vitamin B,, and the hepatic vitamin B,, and the hepatic B,, and the total body vitamin B,,.