English as a Second Language (ESL) PLATO lessons, the students for whom the materials were designed, and the effectiveness of the program at the University of Illinois, Urbana-Champaign, are examined. Two groups of ESL students on the campus have been involved in computer assisted instruction--international students whose native language is not English who have been admitted into degree programs at the university, and nonnative speakers of English attending the Intensive English Institute on the campus and who are not in university degree programs. The lessons have been designed for two levels of students (loosely defined as high and low) and arranged and written to serve as supplementary to the classroom work. Students are assigned four hours of time per week on PLATO, and each unit usually includes four lessons--structure, spelling, dictation, and either a reading or culture lesson. In the two groups, the students are paced through the lessons by a router that will, to an extent, prevent the student from attempting to work with lesson material on PLATO which has not been introduced in class, since PLATO lessons assume prior classroom instruction. The first unit in both programs is a help lesson that provides an introduction to PLATO, the keyboard, the function of the nonletter keys, and the vocabulary used by PLATO to give instructions and to supply feedback. Animation and graphic illustrations have been used in presenting many of the grammar and culture concepts. Games such as crossword puzzles, matching, and word discovery are also used. At present, the lessons only supplement lessons 1-17 of the text, and entail a 16-week study period. The completion of the PLATO lessons to correspond to the text lessons is anticipated. (SW)