The Institute of Pennsylvania Hospital and University of Pennsylvania, Philadelphia, Pennsylvania There is a need for brief, portable performance measures that are free of practice effects but that reliably show the impact of sleep loss on performance during sustained work. Reaction time (RT) tasks hold considerable promise in meeting this need, if the extensive number of responses they typically yield can be processed in ways that quickly provide the essential analyses. While testing the utility of a portable visual RT task during a sustained, quasi-continuous work schedule of 54 h, we developed a microcomputer software system that inputs, edits, transforms, analyzes, and reduces the data from the RT portable audiotapes, for each 10-min trial on the task. With relatively minor modifications, the software system can be used on a minimally configured microcomputer system that supports BASIC. The software is flexible and capable of retrieving distorted data, and it generates a variety of dependent variables reflecting intratrial optimum response capacity, lapsing, and response slowing.