Startle reflex is a very old mechanism that is present in people and rats. It is designed to alert the organism to what might be a potential threat and instigate a rapid response. Startle is a very unique reflex, being dependent on the subject's state and trait. Its amplitude is directly proportional to emotionality. Startle amplitude is significantly greater among Occidental Low Saccharin (LoS) than High Saccharin (HiS) rats and decreases over trial blocks. The present study was conducted to investigate the influence of mild prior stress on acoustic startle in LoS and HiS rats. Eighty-eight HiS and LoS female and male rats (n=11 or 12) were tested in the startle chamber. Half of each group had been mildly stressed (carted around the lab) a week prior to testing. As predicted, LoS rats responded more intensely to the startle test, and startle amplitude decreased over trials. Prior mild stress did increase startle amplitude but only on the third trial - not on earlier or later trials. Contrary to expectations, this effect was similar in LoS and HiS rats. On the first two trials the rats could have been aroused by being in a new environment (the startle chamber), not focusing on the noise. If the startle chamber were not a novel environment the impact of stress could have been more evident. Future research includes manipulating the familiarity of the chamber and intensity of stress, having half the rats spend enough time in the startle chamber so they can be in a familiar environment.