Biomedical research is frequently confronted with regression lines that directionally describe the trend of phenomena, each one represented by a set of correlated x and y data. There could be a need to verify whether the regressions lines of two (or more) phenomena are statistically comparable in their slopes and intercepts, in order to draw conclusions about the similarity or dissimilarity of the conditions under scrutiny. The parallelism test the principles and methodology of which are presented here addresses this problem. A program for microcomputers is supplied as a non-profit software that can be freely shared on the understanding that the copyright belongs to the authors of this article.