The edible blue-green alga (cyanobacterium), Suizenji-nori, contained 143.8+/-22.4 microg of vitamin B(12) per 100 g dry weight of the alga (mean+/-SE, n=4). A corrinoid compound was purified from the dried Suizenji-nori, and partially characterized. The silica gel 60 TLC and reversed-phase HPLC patterns of the purified corrinoid compound were not identical to those of true vitamin B(12), but to those of pseudovitamin B(12) which is inactive for humans.