Presenting the early part of a nonsense sentence in quiet improves recognition of the last keyword of the sentence in a masker, especially a speech masker. This priming effect depends on higher-order processing of the prime information during target-masker segregation. This study investigated whether introducing irrelevant content information into the prime reduces the priming effect. The results showed that presenting the first four syllables (not including the second and third keywords) of the three-keyword target sentence in quiet significantly improved recognition of the second and third keywords in a two-talker-speech masker but not a noise masker, relative to the no-priming condition. Increasing the prime content from four to eight syllables (including the first and second keywords of the target sentence) further improved recognition of the third keyword in either the noise or speech masker. However, if the last four syllables of the eight-syllable prime were replaced by four irrelevant syllables (which did not occur in the target sentence), all the prime-induced speech-recognition improvements disappeared. Thus, knowing the early part of the target sentence mainly reduces informational masking of target speech, possibly by helping listeners attend to the target speech. Increasing the informative content of the prime further improves target-speech recognition probably by reducing the processing load. The reduction of the priming effect by adding irrelevant information to the prime is not due to introducing additional masking of the target speech.