Microcircuit response to nuclear radiations has become an increasingly important concern over the past year. This discussion will consider transient radiation effects (TRE); a companion discussion will cover space radiation effects. The interesting effects occur in two areas: displacement effects resulting from fast neutron irradiation, and ionizing effects caused by prompt pulses composed of x-rays and ??-rays. Fast neutron degradation of microcircuit performance is dominated by transistor current gain reduction. Current gain degradation in microcircuit transistor elements follows the same laws as current gain reduction in discrete transistors of similar base region design and geometry.