The Graduate Record Examinations (GRE) program at Educational Testing Service (ETS) offers tests of subject-matter achievement (GRE Subject Tests) in 17 fields. During the period between June 1982 and September 1984, more than 19,000 non-U.S. citizens and 78,000 U.S. citizens took one of the Subject Tests. This study was undertaken to provide information regarding 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 (for whom English is a second language) are likely to be more proficient at processing the discipline-specific content of GRE Subject Tests in their respective fields than in processing the more general verbal content of the GRE Verbal Test. Based on samples of Subject Test/General Test takers, foreign ESL examinees performed better, relative to U.S. examinees, on Subject Tests than on the GRE Verbal Test, supporting the hypothesis that they should be more proficient at processing discipline-specific English language test content than at processing general English language test content. 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. Research is needed to determine the extent to which the comparative academic performance of U.S. students and foreign students is consistent with their comparative performance on the GRE Subject Tests.