Abstract. Based on Hulstijn and Laufer (2001), a study was carried out consisting of two experiments investigating the involvement load hypothesis in vocabulary learning. Experiment 1 compared the performance of 88 Iranian adult English as foreign language (EFL) learners at the same proficiency level (i.e., high intermediate) to ascertain the effectiveness of three vocabulary tasks with different levels of task-induced involvement. Experiment 2 investigated whether three different tasks which are of different types (input vs. output) but hypothesized to represent the same level of task-induced involvement would result in equivalent initial learning and retention of target words by 56 Iranian adult EFL learners at the same level of proficiency. The results of Experiment 1 showed that the higher level of learner involvement during the task promoted more effective initial learning and better retention of the new words. The findings of Experiment 2 indicated that when different tasks had the same involvement load, they resulted in similar amounts of initial vocabulary learning and retention of new words. The results of the two experiments are discussed in light of the involvement load hypothesis.

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