Two experiments tested the effect of exposure to masked phobic stimuli at a very brief stimulus onset asynchrony on reducing the subjective experience of fear caused by in vivo exposure to a feared object. In the main experiment, 35 spider-fearful and 35 non-fearful participants were identified with a questionnaire and a behavioural avoidance test (BAT) with a live tarantula. One week later, they were individually administered one of two continuous series of masked images: spiders or flowers. They engaged in the BAT again immediately thereafter. They provided ratings of subjective fear at the end of each BAT (pre- and post-manipulation). Very brief exposure to images of spiders reduced the fearful group's and not the non-fearful group's experience of fear at the end of the BAT. This effect was replicated with another sample of 26 spider-fearful participants from the same population. Theoretical implications are discussed.