Twenty-one current regulator systems were built, tested, and put in operation in the Oak Ridge Isochronous Cyclotron. Two motor-generator units rated at 800 and 1200 kW are regulated by transistor banks in the field circuits of the generators. Nineteen other magnet supplies are rectifier-magnetic amplifier systems with ratings ranging from 6 to 30 kW at 250 to 1200 A; for regulation these incorporate transistor banks in series with the load. All units are current regulated to a few parts in 10 5 ; the transistor banks also reduce the ripple voltage of the rectifier units. By means of single controls all units can be varied from 2 to 100% of rated output current. Design features and selection of components for these systems are discussed. Design of the large banks of paralleled transistors used and experience in their operation are also reported.