A study investigated certain mechanisms underlying the acquisition of phrasal verbs in English as a Second Language. Subjects were native Finnish- and Swedish-speaking students in Finland, most aged 16-25 years. The subjects were administered a multiple-choice test with each item containing two correct alternatives, a phrasal verb (preferred by native speakers) and a synonymous one-part verb, and two distractors. Results show that both language groups tended to avoid or under-use English phrasal verbs, but Finns significantly more than Swedes in early stages of learning. The choice pattern among Swedes also reflected a native language pattern. It is argued that both these patterns are indirectly due to first-language influence, but also to the semantic properties of the phrasal and one-part verbs. The data also indicate that the difference in choice pattern found here between Swedes and Finns was evened out with learners who had received considerable natural language input, and that these subjects also showed the most native-like performance in English. Contains 23 tables, 20 figures, and 310 references. (Author/MSE)