Methylcobalamin is one of the two coenzyme forms of vitamin B12. Evidence indicates this form of vitamin B12, in addition to having a theoretical advantage over cyanocobalamin, actually has some metabolic and therapeutic applications not shared by the other forms of vitamin B12. This monograph provides an overview of the pharmacokinetics of methylcobalamin, and will highlight the potential therapeutic relevance for Bell's palsy, cancer, diabetic neuropathy, eye function, heart rate variability, HIV, homocysteinemia, male impotence, and sleep disorders.