This paper examines author productivity as a function of subject breadth using literature-productive engineers--subject breadth is defined as a measure of an author's tendency to move outside one or more closely allied subject areas within a discipline. Subjects for the study were chosen at random from the 1971 author index of The Engineering Index and were traced through the 1972-74 author indexes, giving the study a four-year time frame. Subject fields were determined by using Subject Headings for Engineering. A correlation of productivity with breadth of subject range produced a significant negative correlation. Possible reasons for this production characteristic are discussed. (Author)