Earlier versions of our software sought to combine the functions of data acquisition and display with the processing of previously acquired data that is, to accommodate two users under the simple RT 11 operating system. While, for the most part, a very useful configuration, for more complex flow cytometry where a number of correlated parameters were to be displayed, the histogram memory space was limited. In the current version, data is acquired by a separate pdp 11/23 computer system. Up to three dual-parameter contour displays can be recorded or two contours plus up to four sets of four single-parameter histograms, each of these gated by a separate set of windows. At the end of each acquisition, a full page graphic display is drawn and a hard copy made while numeric data is output to a separate printer all without intervention from the operator who is then free to concentrate on sample injection. The form of data acquired (number of contours, histograms, etc.) can be chosen by the operator at the beginning of each series of analyses as can the format of the graphic display. Alternatively, these settings can be read from an appropriate set-up file stored on disc. List mode data is always temporarily stored on disc for each sample and may be reprocessed with altered windows if desired. The operator may also choose to automatically store list mode data permanently. Interaction with the program is by a set of 22 easily memorized two letter commands, e.g. DC-draw contour, OW-open windows, NF-new file. The data acquisition computer system communicates with the pdp 11/34 data processing and display system via a DR11 C parallel interface for transferring files between the various mass storage devices.