This report aims to show how an emphasis on vocabulary can contribute to courses in English for Specific Purposes (ESP), using the data from two lexical studies. The first study attempts to discover to what extent there may be a general language of science, or semi-technical vocabulary. This type of vocabulary would seem to offer a useful organizing principle for a lexical syllabus in common core ESP courses, and a role for the ESP teacher who finds difficulty in dealing with technical material. The study is concerned with elaborating a definition of the term semi-technical vocabulary using a combination of subjective and objective data, and by applying these criteria to the word list from the LOB Corpus study of a number of scientific disciplines. The second study examines lexical characteristics of one special language, electronics English. It is a lexical needs analysis, attempting to give a group of special interest learners words they need. The study is a count of the frequency items in 20,000 words of electronics English in ten 2,000-word samples. The entire corpus is examined, but the study also focuses on the semi-technical vocabulary of electronics, comparing it with the list developed from the first study. (JL)