An operant arena to study schedule control of the distribution and abundance of rats has recently been described (Goldstein, 1981). Eight rats are free to work for food at anyone of eight operant food stations. A PET Commodore 2001 series microprocessor controls the experiment while an observer records, on the minute, the number of rats observed at each of the eight stations. (For additional experimental control applications by the PET, see Crossman, Williams, & Chambers, 1978;Czerny, 1979;McLean, 1978.) This paper describes the computer programs for the schedule functions controlled by the PET and the analysis of the rat dispersion patterns, controlled by the VAX. An interface between the PET and the operant equipment is described by Blekkenhorst and Goldstein (in press). PET GENERAL PROGRAM DESCRIPTIONThe PET provides simultaneous, independent control over the schedules of reinforcement of all eight stations. It also provides a current update of responses, reinforcements, and momentary status of prevailing schedules on a display that simulates the position of the eight stations in the arena. Further data analyses, including interresponse time (IRT) distribution, mean postreinforcement pause, and the matching relation (Herrnstein, 1970), can also be displayed during or after a session, without interfering with schedule control or data analyses operations. For additional analyses, and as a redundancy measure, all responses and reinforcements are recorded on event recorders that devote two channels to each station and on a cumulative recorder that responds to the input of any combination of all eight stations.