Radioactive 207Bi, produced during nuclear testing at the Pacific Proving Grounds, concentrates in the muscle tissue and organs of goatfish and certain pelagic lagoon fish from Bikini and Enewetak Atolls. It is reasonable to expect that fish capable of accumulating 207Bi could also be efficient accumulators of other bismuth isotopes-namely 210Bi, the daughter of naturally occurring 210Pb. Therefore, 210Bi and consequently 210Po, the decay product of 210Bi, would be expected in notable excess over the precursor 210Pb in specific tissues. To test this assumption, we compared concentrations of 210Pb, 210Bi, and 210POin muscle, liver , and bone separated from some reef species from the Marshall Islands. Concentrations of 210Bi in muscle and liver were found to exceed those of its precursor by factors of2 to 15. The excess 210Bi in some species, however , is not from the environmental sources (either food or water) from which 207Bi is derived. The data suggest that the excess 210Bi may be translocated to muscle and liver tissue following the decay of 210Pb in bone.