The role of phonotactic probability in the segmentation of spoken words in continuous speech was investigated. Participants made speeded word detection responses to sequences of spoken stimuli composed of target words preceded and followed by nonwords (i.e., NONWORD--TARGET WORD--NONWORD). Speed and accuracy of detection were examined as a function of the nonword contexts of the target words. In particular, probabilities of segmental transitions from the nonword contexts to the target words were manipulated: Pairs of segments composed of the last segment of the preceding nonword and the first segment of the target word---as well as pairs composed of the last segment of the target word and the first segment of the following nonword---were varied in terms of intraword transition probability (HIGH and NONE) and transition type (CC, CV, VC, and VV). Both intraword co-occurrence probabilities and transitional probabilities were manipulated. The implications of the results for the use of phonotactic probabilities in the identification of words in fluent speech will be discussed.