In the relatedness proportion effect, semantic priming increases with an increase in the probability that a word prime will be followed by a semantically related word target. This effect has frequently been obtained in the lexical decision task but not in a pronunciation task. In the present experiment, relatedness proportion was manipulated in two pronunciation tasks, one with and one without nonword targets, using category names as primes. In both tasks, a relatedness proportion effect occurred for high-dominance category exemplars but not for low-dominance category exemplars. These results converge with recent lexical decision results in suggesting that semantic priming in pronunciation is affected by a prospective prime-generated expectancy that is modulated by the relatedness proportion.In the semantic priming effect, responses are faster and/or more accurate when a target word is preceded or accompanied by a semantically related prime rather than an unrelated prime (e.g., see Meyer & Schvaneveldt, 1971;Neely, 1976; see also Neely, in press, for a review). In the lexical decision task (LDT), in which subjects make word/nonword decisions about the target, semantic priming effects increase in size as the proportion of related word-prime/word-target trials (the relatedness proportion) increases (e.g., see de Groot, 1984;den Heyer, 1985;den Heyer, Briand, & Dannenbring, 1983;Neely, Keefe, & Ross, 1989;Seidenberg, Waters, Sanders, & Langer, 1984;Tweedy, Lapinski, & Schvaneveldt, 1977). In the present research, we test Neely and and Neely et al. 's (1989) theoretical analysis of the two mechanisms responsible for this relatedness proportion effect (hereafter RPE) in the LDT.Portions of this research were presented at the 1984 and 1988 meetings of the Midwestern Psychological Society in Chicago and were conducted by Dennis E. Keefe in partial fulfillment of the requirements for the MS degree at Purdue University, under the direction of James H. Neely. We thank Henry L. Roediger III and Richard Schweickert, who also served on the MS committee. We also thank Gordon Logan and David Balota for their helpful comments. Finally, we thank Kim Brady and Kent Ross for testing some of the subjects.