The present study investigated the influence of word processing on the writing of students of English as a second language (ESL) and on writing assessment as well. Twenty-one adult Mandarin-Chinese speakers with advanced English proficiency living in Toronto participated in the study. Each participant wrote two comparable writing tasks under exam-type conditions--one on a Macintosh computer that traced and recorded their writing and revision processes and the other written with pen. Think-aloud protocols were also recorded. It was found that participants paid more attention to higher order thinking activities while evaluating their written texts in the computer session, that they revised significantly more at most levels on the computer, and that their computer-generated essays received higher scores in argumentation than the hand-written ones, suggesting that educators should seriously consider the impact of computers on writing assessment. (Contains 5 tables.)