The authors' goal was to examine the structural relationships among vocabulary knowledge, morphological awareness, syntactic awareness, and reading comprehension in English-speaking adults. Structural equation analysis of data collected from 151 participants revealed that morphological awareness affected reading comprehension directly. Syntactic awareness predicted reading comprehension not only directly but also indirectly via vocabulary knowledge. Vocabulary knowledge made an independent contribution to reading comprehension above and beyond those of morphologic awareness and syntactic awareness. (Contains 4 tables and 3 figures.)