Three BASIC programs for processing observational, nonconcurrent sequential data are presented. The programs follow Sackett’s lag sequential analysis method and have the innovations of running on interactional microcomputers and of providing plots of results. The outcome of the analysis is stored on a magnetic disk, facilitating a further application of probabilistic models to the transformed data. The Allison-Liker correction for the comparison test between expected and observed lag probabilities is included in the programs.