The purpose of the present study was to provide empirical support for the construct of the involvement load hypothesis (ILH ) in an EFL context. To fulfill the purpose of the study, 4 intact groups consisting of 126 intermediate-level students participated in this experiment. In order to ensure that the participants were at the same level of English language proficiency, the Nelson test was administered prior to the treatment. Moreover, the participants were pretested on the knowledge of the target items through the Vocabulary Knowledge Scale (VKS). During the 7 treatment sessions, the 4 groups were treated with different tasks (reading, fill-in-the-blanks, sentence-writing, and composition-writing) varying in the involvement index according to the ILH. The VKS was administered twice (immediate and delayed posttests) to measure the gain degree at receptive and productive levels. The results indicated the validity of the hypothesis in receptive and productive learning and receptive retention. In productive retention, however, partial support for the hypothesis was provided. In addition, vocabulary gain in partially known, receptive, and productive categories could lend support to the effectiveness of each treatment over time.