P. mirabilis and P. vulgaris are the two wellknown species in the genus Proteus. P. myxofaciens and P. penneri are recent additions to the genus. We isolated P. penneri from the pus of a patient with suppurative otitis media and an epidural abscess. The characteristics of the organism, including morphology, staining, physiology and biochemistry, were studied. Clinical microbiological laboratories should suspect P. penneri in the case of as Proteus strain that is negative for indole, salicin and esculin, but otherwise resembles P. vulgaris. Proteus penneri, formerly known as Proteus vulgaris indole-negative or as Proteus vulgaris biogroup 1, was named by Hickman et al in 1932. Little information about human infection by this organism is available. In 1982, Hickman and co-workers studied 20 strain of P. penneri which were isolated from clinical specimens (urine, stool, etc.) in the USA. However, its clinical significance, until recently, was unknown. We isolated a strain of P. penneri from the pus of a patient with suppurative otitis media and an epidural abscess on June 10 and 15, 1989. This paper concerns the problems encountered in identifying this organism and its clinical significance.