The Graduate Record Examination (GRE) subject-matter achievement tests are offered in 17 fields. This study investigated the performance of U.S. and non-U.S. citizens on the Subject Tests, and the relationship of selected English-proficiency-related background variables to the test performance of non-U.S. citizens. It was also concerned with exploring the hypothesis that foreign ESL examinees are likely to be more proficient at processing the discipline-specific content of GRE Subject Tests in their respective fields than in the verbal content of the GRE Verbal Test. Data were collected primarily from GRE files of all examinees who took the Subject Tests between October 1982 and September 1984, and who answered a question on citizenship status. Profiles of GRE Subject Test means were developed for U.S. and non-U.S. examinees, generally, and in classifications that introduced some controls for differences in English language background linked to country of origin. Non-U.S. examinees generally had higher means than U.S. examinees on Subject Tests in Spanish, French, Music, Psychology, Mathematics, Computer Science, Chemistry, Physics, and Economics, and slightly lower means in Engineering and Sociology. U.S. citizens had clearly higher means in Geology, Biology, Education, Political Science, History, and Literature. A major implication of the findings is that scores on the GRE Subject Tests appear to be useful for assessing relative levels of subject-matter mastery for examinees differing widely in linguistic-cultural-educational background. (Author/JAZ)