The penicillin-binding protein (PBP) profile of Haemophilus ducreyi was determined by a whole-cell-labeling assay. Only two major PBPs, of molecular weights 90,000 (PBP 1) and 38,500 (PBP 2), were detected in six of eight strains studied. Competition binding experiments and the attendant morphological effects suggested that PBP 1 was either a functional amalgamation or a lack of resolution of two proteins equivalent to PBPs 1 and 3 of Escherichia coli.