A study investigated how Hispanic bilingual students' knowledge of Spanish vocabulary and awareness of Spanish-English cognates influence comprehension of English expository text. The subjects, 74 upper elementary school students literate in both Spanish and English, were tested for vocabulary knowledge in both languages. After reading four expository texts containing English words with Spanish cognates (e.g., English "transform" and Spanish "transformar"), subjects were given a multiple-choice test for understanding of key concepts from the texts. After a brief explanation of the concept of cognates, they were asked to identify words in the text with Spanish cognates. Results indicate the following: (1) the students were aware of cognates and made some use of that knowledge in their English reading; (2) the contribution of Spanish vocabulary knowledge to English reading is not automatic, but depends on the degree of awareness of the languages' cognate relationship; and (3) student knowledge of cognates could be even greater, suggesting that explicit instruction in cognates may be useful. Further research on the nature of student understanding of cognates is recommended. Appended materials include a sample multiple-choice test item, statistical results of the study, a sample passage and related questions, a list of target cognates, and the cognate-circling task. (MSE)