Abstract

Evidence is presented that after injection of radioactive vitamin B₁₂ in man, there is a close correlation between the amount of radioactivity excreted and the amount of assayable vitamin B₁₂ excreted, and thus that the amount of radioactivity excreted is a true measure of the vitamin B₁₂ excreted. The possible reasons for this occurrence are discussed and it is suggested that in the body vitamin B₁₂ does not exist as such but as an analogue or active derivative.