B12 analogues, homocysteine, methylmalonic acid (MMA), and unsaturated transcobalamins, all potential markers of vitamin B12 status, were analyzed in blood and cerebrospinal fluid (CSF) from 22 patients with primary degenerative dementia of Alzheimer type. The level of active vitamin B12 in serum correlated significantly with serum homocysteine, serum MMA, and CSF homocysteine. CSF B12 correlated significantly with serum homocysteine and serum MMA. The ratio of analogues and active vitamin B12 concentrations in serum (analogue/active B12 ratio) correlated significantly with serum homocysteine, serum MMA and CSF B12. This study had no control group. However, based on available reference values, high concentrations of homocysteine and MMA in serum and unsaturated transcobalamin II in plasma were interpreted as evidence of vitamin B12 depletion or deficiency. Such high concentrations were found in a significant number of patients. In 9 patients, vitamin B12 injections were administered. After treatment, serum homocysteine levels fell significantly. We conclude that vitamin B12 analogues, homocysteine, MMA, and transcobalamins may be useful as markers in studies aimed at clarifying the role of vitamin B12 deficiency in dementia disorders.