General startle reactivity reflects defensive reactivity independent of affective foreground. We examined the relationship between general startle reactivity and startle response to threat in three tasks with distinct manipulations of threat uncertainty. General startle reactivity was a stronger predictor of startle response during threat (vs. no threat) and uncertain (vs. certain threat). These results confirm that including general startle reactivity in our analyses can increase the power and/or precision to test effects of other focal experimental manipulations or grouping variables. Moreover, this suggests that individual differences in defensive reactivity moderate responding to threats of various types in our environment. As such, individual differences in general startle reactivity may index important psychological attributes related to trait affectivity, premorbid vulnerability for psychopathology, and manifest psychopathology.