Three programs are described for evaluating and characterising data collected during numerical taxonomic studies of bacteria. The program VARIANCE compares replicate cultures and evaluates the reproducibility of each character. Also it identifies those characters that should be excluded from subsequent taxonomic analysis because of their poor reproducibility. GPROPS summarises the properties of clusters of strains that have been defined from a cluster analysis, it can produce a probabilistic identification matrix and compares each strain within a cluster with the Hypothetical Mean Organism (HMO) of that cluster. OVCLUST is an implementation of the program described by Sneath (1979) which calculates overlap statistics between major clusters. These programs are designed to complement the CLUSTAN package (Wishart, 1982) which is often used for cluster analysis of bacterial taxonomic data. The programs were written in FORTRAN 77 and implemented on an IBM PC using MS-DOS.