The hematology of tunicates, a class of common marine organisms that selectively accumulate metals such as V, Fe, Mo, Nb, has puzzled scientists for over 70 years. The black tunicate Ascidia nigra (Linnaeus) sequesters vanadium as the pentavalent vanadate, concentrates it by 106-fold, and stores the metal in its reduced V(III) or V(IV) states at physiological pH (ca. 7.2), possibly as a hexaaquo or other complex. The apparent contradiction that V(III) is unstable in aqueous media at pH above 2.5 can be overcome by assuming the presence of a strong reductant that also serves as a good complexing agent. We believe that this role is fulfilled by the tunichromes, the bright yellow blood pigments of A. nigra, and various other tunicates. Tunichromes, especially in the crude state, are extremely labile, consist of a complex mixture of closely related compounds, and have eluded all isolation attempts. We report the isolation and characterization of tunichrome B-1 (TB-1), the first member of a group of new biological reducing agents. We report reversible permeability control through a viologen (4,4'-bipyridinium)-containing bilayer-film deposited on a platinum minigrid sheet by electrochemical redox reactions. Developments of various types of permeability-controllable membranes have been prompted by the need to study the transport properties of biological membranes. We have reported the signal-receptive, bilayer-coated capsule membranes, in which bilayers supported on the physically strong polymer membrane act as a valve of slow releases from the capsule responding to stimuli from the outside. Kunitake, Kajiyama, and co-workers recently prepared various types of the bilayer-immobilized films and reported that the permeability across the bilayer- or liquidcrystal-immobilized film could be changed by phase transition phenomena and photoirradiation. We also observed the permeability of the bilayer film could be regulated by the electric transmembrane potential. Burgmayer and Murray first reported that the permeability of anions through a polypyrrole film deposited on a Au grid could be changed by positive charge formation on the film by electrochemical redox reactions.