A discriminator circuit for use with millimicrosecond counting equipment is described here. The circuit utilizes a diode voltage comparator which drives a secondary‐emission tube univibrator after amplification. Two shaped outputs are provided: one, of short duration, for use with 10‐Mc scalers, and another longer pulse for microsecond scalers.The main characteristics of this unit are its good response to pulses as short as 3 m &mgr;sec and the fast recovery time, which is less than 0.1 &mgr;sec at the fast output.