We investigated the efficacy of oral vitamin B12 (B12) therapy in patients with B12-deficiency anemia. Between June 1994 and June 2000, 17 patients, who were diagnosed as having B12-deficiency anemia and gave their informed consent, were enrolled in this study. Of these patients, 7 were further treated with a maintenance dose of methylcobalamin (1,500 micrograms daily for 7 days every 1-3 months). Correction of hematological and neurological abnormalities was prompt. The hemoglobin level and serum concentration of B12 were normalized within two months after starting the treatment. Recovery from neurological disturbance was observed within one month. To maintain a normal serum concentration of B12, a 7-day regime of administration was needed every month in 3 patients, every 2 months in 3 patients, and every 3 months in 1 patient. These results demonstrate the effectiveness of oral cobalamin therapy, and also that oral intermittent therapy is useful for maintaining a normal serum B12 concentration. Oral cobalamin therapy might be as effective as conventional injection therapy, and useful for long-term treatment.