A data processing circuit implemented in 2.5 μm Josephson Current Injection Logic (CIL) has been designed and successfully tested at subnanosecond cycle times, corresponding to a data processing rate of over 1 Gigabit per second. The circuit was implemented using a total of 177 devices (102 logic gates), and is the most complex Josephson logic circuit operated so far. The minimum cycle time achieved was 665 ps (5 logic stages), the corresponding chip power dissipation being about 350 μW. The performance was ultimately limited by variations in junction critical currents and resistor values that were larger than the design values. Copyright © 1982 by The Institute of Electrical and Electronics Engineers, Inc.