Sudden onset inspiratory occlusion stimuli elicit large amplitude P300 components and also startle blinks. The primary purpose of this study was to assess the influence of the startle reflex on the respiratory related P300. A secondary purpose was to assess changes in P300 scalp topography as a function of stimulus familiarity. Young adults (n=12) were exposed to 200 inspiratory occlusion stimuli, and EEG was recorded from 29 A1/A2 referenced sites. Data from the occlusions were divided into four consecutive blocks of 50 trials to assess blink and P300 habituation effects. Results showed that 40% of the occlusion stimuli elicited a blink response, and that blink amplitude showed significant habituation across the experimental session. Change in P300 amplitude across the experimental session varied according to scalp site. At central and parietal locations, P300 amplitude showed an initial decrease but then remained stable. Frontally, P300 amplitude decreased over each of the four trial blocks. P300 scalp topography showed a classic centro-parietal maximum, however, a more frontally orientated scalp focus was seen for the first trial block. P300 was not significantly different when derived from averages of responses containing and not containing blinks. These data indicate that the previously studied centro-parietal P300 is not related to a startle reflex. However, when occlusions are first presented, a scalp topography similar to that previously noted for novel stimuli is observed.