Low RC time constants, small physical size, low operating voltages, and, in many units, a current gain in excess of unity make transistors promising for trigger-circuit applications. Trigger action can be obtained with a single transistor if its current gain exceeds unity. Mathematical analysis indicates the possibility of triggering with successive pulses of the same polarity by use of an additional crystal diode. Improvement in some respects is obtained if a transistor is used in conjunction with a vacuum-tube cathode follower.