Some species of the cyanobacteria, including Spirulina, Aphanizomenon, and Nostoc,are produced at annual rates of 500–3000 tons for food and pharmaceutical industries worldwide (61). Tablets containing Spirulina sp. are sold as a health food fad, since it is known to contain a large amount of vitamin B12 (62). We found that commercially available spirulina tablets contained 127–244 μg vitamin B12 per 100 g weight (63). When two corrinoid compounds were characterized from the spirulina tablets, the major (83%) and minor (17%) compounds were identified as pseudovitamin B12(adeninly cobamide) and vitamin B12, respectively (Fig. 2⇓). Several groups of investigators indicated that pseudovitamin B12 is hardly absorbed in mammalian intestine with a low affinity to IF (64, 65). Furthermore, researchers showed that spirulina vitamin B12 may not be bioavailable in mammals (63, 66). Herbert (67) reported that an extract of spirulina contains two vitamin B12 compounds that can block the metabolism of vitamin B12. And van den Berg et al. (68) demonstrated that a supplemented diet does not induce severe vitamin B12 deficiency in rats, implying that the feeding of spirulina may not interfere with the vitamin B12metabolism. Further studies are needed to clarify bio availability of spirulina vitamin B12 in humans.