The present study tested the hypothesis that briefly flashed and backwardly masked phobic stimuli potentiate startle reflexes in phobic subjects. Spider phobic (n = 17) and normal control (n = 12) subjects were exposed to short (30 ms) and backwardly masked presentations of phobic slides (i.e., spiders) and neutral slides (i.e., flowers, mushrooms, snakes). On half the trials, eyeblink startle reflexes were elicited with auditory probes following presentation of the slides. In spite of the degraded stimulus conditions, there were some indications that phobics exhibited a startle pattern different from control subjects. More specifically, phobic subjects tended to react with larger startles during the second block of spider trials than control subjects. No such group differences were found for the neutral trials. As the eyeblink startle reflex is closely linked to the thalamo-amygdala pathway, the present findings provide some preliminary support for the idea that the preattentive processing of phobic cues is located at the subcortical level.