Linguistic competences are of foremost importance to students in ESP (English for Specific Purposes) programs where they receive training in areas such as vocabulary, sentence structure and rhetoric norms common to science engineering fields in order to function professionally in English in an increasingly international environment. To achieve this goal, students have to be nurtured in field-specific language contexts - an aim which is more focused than General English or English for Academic Purposes approaches. To this end, ESP instructors attempt to find effective methods to analyze student abilities and tailor materials suited to their needs and level of proficiency. This paper describes the first part of a longitudinal project which aims to improve vocabulary development of third-year science engineering students in a Japanese university. In this pilot study, one third of the classes of undergraduate Technical English were given the vocabulary size test developed by Paul Nation and David Beglar (2007) to gauge students' approximate vocabulary size for general English reading. The 30-minute test was administered in class via the university's e-learning system (WebClass UEC) to expedite the compiling of results. This presentation reports the background and rationale for using this particular measurement, the holistic results of the pilot assessment, the analysis of the correlations and deviations between departments, and the implications of these similarities and differences. In addition, these results will be used for deciding on the level from which to develop teaching materials to bridge the gaps that may appear in students' semi-technical and technical lexical repertoire. In future studies, these results will be correlated with TOEIC scores of the same students, as well as the results of other academic and specialized technical word lists.