A preliminary report on a long-term empirical investigation of advanced language acquisition in a study-abroad environment is presented. The project is based on an American Council of Teachers of Russian (ACTR) longitudinal study of the gains in Russian language competence demonstrated by American students in semester-long language programs in Moscow and Leningrad. Six-year data include student information on age, gender, citizenship, country of birth, place and levels of formal education, and information on all prior training in the Russian language. Analysis of test results in oral, listening, and reading proficiency shows that the immersion experience produces significant gains in language proficiency achieved by a variety of American college-level learners of Russian. One of the conclusions is that at any given initial level, the better prepared the student is on reading/grammar the more the student tends to gain. Also, the Modern Foreign Language Aptitude Test (MLAT) is shown to be a valid predictor of success in developing reading and listening skills in Russian, although it does not serve to predict oral proficiency gain as measured by the standard Oral Proficiency Interview (OPI). Another finding is that the gains are significantly higher for males than for females, a phenomenon that may be influenced by communication interactions in-country. Contains 13 references. (LB)