Abstract The present study applied empirical clustering procedures to the MMPI protocols of 196 chronic phencyclidine (PCP) abusers. Subjects were randomly divided into two groups, and two methods of cluster analysis, the average linkage method and Ward's hierarchical procedure, were performed. Both cluster methods produced highly comparable results within each group, and the MMPI profiles found in each group were quite similar. Cluster analytic studies of other substance abuse populations are needed in order to replicate the MMPI profile types found in the present study. These investigations would lead to an empirical typology across various substance abuse populations that would depict developmental stages.