Vitamin B12 content of various edible shellfish was determined by both Lactobacillus leichmannii ATCC 7830 microbiological and intrinsic factor-chemiluminescence methods. The values determined by the microbiological method were 1.2-19.8 (M/C ratio) fold greater in the shellfish than the values determined by the chemiluminescence method. Vitamin B12 compounds were purified from most eaten shellfish, oyster (M/C, 1.5), mussel (M/C, 1.2), and short-necked clam (M/C, 2.7), and partially characterized. TLC and HPLC patterns of each red-colored vitamin B12 compound (M/C, 1.0-1.2) purified from these shellfish were identical to those of authentic vitamin B12. Although the higher values in the determination of vitamin B12 by the microbiological method may be due to the occurrence of vitamin B12-substitutive compounds, the edible shellfish would be excellent vitamin B12 sources judging from the values (> or = 6 micrograms/100 g) determined by the chemiluminescence method.