Prepulse inhibition (PPI) and habituation of the startle response are operational measures of sensorimotor gating and information processing. Changes in the normal inhibition and habituation of the startle response may provide trait markers for illnesses such as schizophrenia that have altered neurotransmitter control of the neural circuitry that modulates these measures. The stability of PPI and habituation was assessed in 10 normal male subjects. Prepulse inhibition was found to be most stable in the more intense prepulse conditions, and habituation was most stable in the early portion of the test session. These data support the hypothesis that PPI and habituation are relatively stable neurobiological markers.