A program written in TELCOMP, an interactive-computer language, is presented for doing all the necessary computations for the Johnson-Neyman (1936) technique in the simplest case, starting from raw sums, sums of squares, and sums of cross-products or from means, standard deviations, and correlations previously computed for the two groups. Computations are shown for three sets of data, two of which are from previous expositions of the method; it is noted that these previous expositions suffered from computational errors of major seriousness. The third set of data illustrates use of the method for investigating interactions between individual differences and treatments in such a way as to supplement the usual analysis of covariance procedures.