This paper describes a computer program designed to look for similarities between pairs of nucleic or amino acid sequences. The program looks both for segments of perfect identity or for regions where, using a scoring matrix, a minimum value is exceeded. The results of comparisons are presented as a matrix which is displayed on a simple graphics terminal. Use of a graphics terminal allows the user to display the whole of the two sequences in one screenful or to home-in on regions of interest to examine them in more detail. The program is interactive and so the user can easily see the effect of changes to variables and can use inbuilt editing functions to make insertions to produce alignments of the two sequences. These aligned sequences can then be saved on disk files for further processing.