  We have investigated the magnetic field-induced metal-insulator transition in
the tau-phase organic conductors, which occurs in fields above 35 T, and below
14 K, by magnetization, thermoelectric, and pressure dependent transport
methods. Our results show that the transition is a bulk thermodynamic process
where a magnetic field-dependent gap opens upon entry into the insulating
state. We argue that the transition involves a magnetic field-induced change in
the electronic structure.
