Recent stimulus-response formulations have indicated that similarity between persons functions as an unconditioned stimulus (UCS) and that interpersonal attraction is a classically conditioned evaluative response. The thesis of this study is that similarity is a correlate of evaluative meaning and that the latter rather than the former is responsible for conditioning. The Staats conditioning procedure was used with trigrams as conditioned stimuli (CS) and personality-trait adjectives as unconditioned stimuli (UCS). The UCS adjectives were previously rated on evaluation and similarity scales, and these variables were held constant across levels of each other in a 2 x 2 within subjects (Ss) design. In support of the hypothesis, it was found that for 89 pretested Ss evaluation and similarity were highly correlated (.879) and that for the 16 Ss in the conditioning procedure an evaluative response to trigrams was influenced by evaluation (p<.005) but not by similarity (p>.20). (Author/DO)