This study investigated the effects of second language (L2) proficiency and task-induced cognitive workload on participants' speech production and retention of information in an environment designed to simulate the demands faced by pilots receiving instructions from air-traffic controllers. Three groups of 20 participants (one native-English-speaking group, two native-Mandarin-speaking groups of relatively high and low levels of English proficiency) played the role of pilots. Participants listened to, repeated, and responded to simulated air-traffic controller messages (in English) under conditions of low and high workload. In the high workload condition, participants performed a concurrent arithmetic task while repeating the messages. The dependent variables were message repetition accuracy and speech production (accentedness, comprehensibility, fluency, as perceived by 10 native-English-speaking raters). The native English speaker group repeated messages more accurately than both L2 groups, and the low-proficiency group repeated messages less accurately in the high workload condition than in the low workload condition. The native speaker and the low-proficiency groups were perceived as less fluent in the high than in the low workload condition, and only the low-proficiency group's speech was perceived as more accented in the high than in the low workload condition. Implications for language training and assessment for English for specific purposes are discussed. (Contains 3 tables and 1 footnote.)