This study investigated the relationship between aptitude, as measured by Defense Language Aptitude Battery (DLAB) scores, and oral proficiency as measured by the Oral Proficiency Interview (OPI) scores of 72 Federal Bureau of Investigation (FBI) Special Agents who completed basic foreign language training at the Defense Language Institute (DLI). The hypothesis that the DLAB is a predictor of proficiency levels resulting from DLI training was not strongly sustained, as 40% of the Special Agents fell below the level 2 training goal, and because many of the Special Agents who received low OPI scores received the highest aptitude scores. Self-assessment data on their language learning success were collected from 76 former students, and the following factors were identified as most influential to success: (1) motivation/perseverance; (2) instructor; and (3) personal ability/aptitude. Factors having a negative influence on language learning success included: (1) poor quality of materials; and (2) inappropriate grammar/vocabulary. (DJD)