Emotion-modulated startle reflex is an important indicator of traitlike differences in affective processing implicated in the biological basis of personality and psychopathology. This study examined heritability of startle modulation by affective pictures in 66 pairs of monozygotic and 57 pairs of dizygotic female twins. Consistent with previous studies, startle magnitude was significantly influenced by emotional valence of the picture (positive<neutral<negative). Absolute response magnitude showed high heritability in all three valence conditions (59–61%); however, there were no significant genetic influences on the amount of startle modulation. Thus, our data do not support the hypothesis that emotion-modulated startle can serve as an indicator of genetically transmitted individual differences in affective processing.