Ensuring second language (L2) learners have an adequate breadth and depth of L2 vocabulary knowledge is a key pedagogical objective in L2 learning contexts. For this reason, establishing guiding principles that successfully enhance the efficacy of L2 vocabulary knowledge development is of strong importance. The current study investigated the value of applying principles from the Involvement Load Hypothesis (ILH) as part of a reading comprehension task among 40 intermediate English as a foreign language (EFL) students. Half of the group undertook a high involvement reading task, whereas the other half undertook a low involvement reading task. After the reading task, an unannounced Vocabulary Knowledge Scale test was administered to measure incidental vocabulary gains. Results showed the high involvement group remarkably outflanked the low involvement groups in terms of the target words learned from the reading task. A delayed post-test indicated that the retention of target word knowledge was more robust among the high involvement group, but that this difference did not maintain a level of statistical significance after 2 weeks. We conclude with suggestions about how EFL/ESL instructors can apply the principles of the ILH in efforts to systematically enhance learners’ L2 vocabulary knowledge.