The majority of recent publications on the immunology ofPropionibacterium acnesrelate to the potential use of the bacterium as an adjuvant or its use in rodent models of human inflammatory disease. These studies have increased the understanding of the potential effects ofPropionibacterium acneson cells of the mononuclear phagocyte system. Research into the immunology of acne and the role thatPropionibacterium acnesplays in inflammatory acne has been limited, with efforts being focussed on the problems ofPropionibacterium acnesresistance to antibiotics. Recent studies have indicated that inflammatory acne is a T cell-mediated disease, but whetherPropionibacterium acnesis the initial stimulus for either the specific or non-specific recruitment of T cells in acne lesions is still a matter for conjecture.