Summary (1) Four patients with pernicious anemia in relapse were treated with 1 μg of crystalline vit. B12 intramuscularly, daily. Three cases showed submaximal reticulocyte responses and failed to reach normal blood levels in 53 to 93 days. Clinical improvement was observed in all instances. (2) Four other patients with pernicious anemia in relapse, treated with 2 μg of crystalline vit. B12, intramuscularly, daily, showed satisfactory clinical improvement, optimal reticulocyte responses, and normal blood levels in 48 to 69 days. Symptoms of neurologic disease disappeared in one person but persistent signs were observed in all 4 cases.