An interactive computer program, SWELL, displayss and analyzes bivariate distributions generated by flow cytometers. SWELL is modular with options available via a menu, is written in Fortran, and utilizes a video color display system. Data are accumulated as a bivariate distribution that is transferred to the computer as a 64 x 64 matrix. For ease of visualization, matrices are displayed in pseudocolor. The distribution values are broken into eight ranges and each range is represented by a color. Each element of the matrix is then displayed in its assigned color. To allow pooling and comparison, distributions are aligned, edited, and standardized. Unknown samples are pooled or analyzed singly and compared to the normal pool by subtraction. Differences are displayed as pseudocolor matrices of sign, magnitude, or statistical magnitude in units of standard deviation. This latter display, scaled to tolerance limits, readily reveals regions of significant difference between normal and abnormal samples. Counts within such regions can be compared to diagnose samples automatically.