purpose: The purpose of this study was to assay serum cobalamin levels in patients with systemic lupus erythematosus (SLE) as there are few case reports on the association of pernicious anemia and SLE. patients and methods: Serum cobalamin levels were assayed in 43 female SLE patients by a radio-dilution assay using purified intrinsic factor. results: Cobalamin levels were found to be significantly lower in the SLE group compared with a normal control group, eight of whom (18.6%) had serum cobalamin levels equal to or lower than 180 pg/mL (mean: 129.25 ± 40.05 pg/mL). None of the SLE patients had been found to have pernicious anemia. The transcobalamin II level and unsaturated vitamin B12 binding capacity, but not the cobalamin level, were positively correlated with SLE activity. conclusions: Our results may indicate a subtle cobalamin deficiency in SLE patients without pernicious anemia.