The objective of this study is to investigate how low-proficiency English for Specific Purposes (ESP) students benefit from a hypermedia-enhanced learning environment, specifically in terms of incidental acquisition of lexical items in the target language. Additionally, this study aims at finding out how frequently the comprehension tools available from within the application were used by the learners. The hypermedia-assisted learning environment used in this study provides a rich environment where learners gain exposure to foreign language texts by listening and reading in the target language. Learners are invited to explore Chemistry-related video segments through listening comprehension questions in combination with access to various comprehension tools, for example, L1 translations of questions and answers, L2 video manuscript, translation of manuscript sentences, specific video segments containing answers to questions and video control tools. A total of 40 subjects with a low-intermediate proficiency level were exposed to the treatment. An achievement test was administered before the treatment as a pre-test, and two weeks following the completion of the treatment as a post-test, to evaluate retention. The courseware was set up by the researcher to record every user action and compile these data into user logs of behaviour data which were subsequently submitted to analysis. The findings of this experimental study are conclusive in suggesting that hypermedia-based instruction can provide an effective learning environment to build vocabulary among ESP students. It can be claimed that the access to a variety of comprehension tools results in a deep processing of the lexical items and can therefore contribute to favour retention.