The role of specific micro-organisms in producing chronic wound malodour was investigated by directly comparing odour severity and microbiology in infected and non-infected leg ulcers. Malodour was most frequently associated with infected wounds involving mixed aerobic and anaerobic, Gram-positive and Gram-negative microbial populations. Infected ulcers that were not characterised by an offensive odour were rarely colonised with anaerobic bacteria. A reduced incidence of pigmented and non-pigmented Gram-negative anaerobes (Bacteriodes spp, Prevotella spp, Porphyromonas spp) was evident in non-infected, non-malodorous leg ulcers. These observations emphasise the significance of specific anaerobic bacteria in the generation of wound malodour, and it is probable that their effect is potentiated by coexistence with mixed facultative micro-organisms.