Presents a spreading-activation theory of human semantic processing, which can be applied to a wide range of recent experimental results. The theory is based on M. R. Quillian's (1967) theory of semantic memory search and semantic preparation, or priming. In conjunction with this, several misconceptions concerning Quillian's theory are discussed. A number of additional assumptions are proposed for his theory to apply it to recent experiments. The present paper shows how the extended theory can account for results of several production experiments by E. F. Loftus, J. F. Juola and R. C. Atkinson's (1971) multiple-category experiment, C. Conrad's (1972) sentence-verification experiments, and several categorization experiments on the effect of semantic relatedness and typicality by K. J. Holyoak and A. L. Glass (1975), L. J. Rips et al (1973), and E. Rosch (1973). The paper also provides a critique of the Rips et al model for categorization judgments.