Abstract. This study examined the effects of vocabulary pre-instruction on reading comprehension. Two vocabulary training treatments, chosen on the basis of a theoretical framework for vocabulary instruction, and a control were used with 28 average fifth-grade readers. For two of three order groups, both training treatments produced significantly higher scores on passage tests, and, for all children, both training treatments produced significantly higher scores on two sentence comprehension measures and a multiple-choice synonym test, indicating that pre-instruction had a significant effect on both comprehension and vocabulary learning. In addition, a mixed method of vocabulary instruction, or one which provided both definitional and contextual information about the taught words, produced significantly higher comprehension scores than did a definitional method.The relationship between word knowledge and reading comprehension is one of the best documented relationships in reading research. Although research in factor analysis (Davis, 1944;Spearitt, 1972), readability (Chall, 1958; Klare, 1974 Klare, -1975, and test construction (Fair, 1969) has consistently found a strong correlation between vocabulary knowledge and reading comprehension, there has been little agreement as to the reason for this correlation. Anderson and Freebody (1981) suggest three hypotheses which