Family physicians frequently advise their patients on choosing and implementing regular programs of exercise. This report describes techniques of submaximal aerobic fitness assessment and microcomputer-assisted exercise prescription suitable for use in office-based practice. A submaximal bench step test is used for the estimation of aerobic fitness. A BASIC program operating on a Macintosh provides calculations of fitness levels and produces an individualized exercise prescription. While obviously not suitable for every patient, this approach is practical for young to middle-aged low-risk individuals interested in beginning regular training programs.