Odour problems related to mushroom composting have been reviewed and compounds implicated in odour production have been identified. Troublesome compounds characterised included thiols, sulfides, amines, ammonia, and organic acids. Protein metabolism, especially of the methionine component, appears to be critical to the production of odouriferous compounds. Factors contributing to odours were identified, some of which may be obviated through processing modifications. Odour problems might be reduced by decreasing the amounts of nitrogen and sulfur used in the initial compost mixture, maintaining more aerobic processing conditions, and preventing inhibitive temperatures (>60�C) being achieved.