Plutonium-237 distribution and translocation in channel catfish following intracardial injection are basically similar to patterns in mammals after intraveneous administration. Bone and liver are the dominant contributors to the body burden. The fractional body burdens in bone, liver, and kidney 17 days after injection were 31, 24 and 9% of the injected dose, respectively. High kidney burdens relative to mammals are expected since the kidney functions as the major site of hemopoeisis in teleosts. The observation of high concentrations in some ovaries, coupled with apparent polymorphism in plutonium-binding plasma proteins, suggests that some aspects of plutonium transport in blood of lower vertebrates may differ significantly from the mammals. Excretion over the 17-day period was 510%. The absence of significant excretion indicates that a short half-life component of elimination following gut clearance in earlier gavage studies is due to plutonium labeling of the gut.