The literature covered by this review deals with microbiological attack on organic sulphur-containing hydrocarbons, often represented by the model heterocyclic compound, dibenzothiophene. The objective of most research in this area is to find suitable biocatalysts for removal at the industrial scale of organic sulphur from fossil fuels. Ideally, microbes for desulphurisation should attack the sulphur in hydrocarbons without altering the carbon skeleton or affecting other valuable components of the oil or coal. Organisms able to cleave carbon-sulphur bonds releasing sulphur atoms (as sulphate in aerobic mechanisms or hydrogen sulphide in anaerobic processes) appear to fulfil these requirements. Biodesulphurisation mechanisms which convert sulphur heterocycles into water-soluble oxidation products could cause the loss of the hydrocarbons associated with the sulphur hetero atom from the bulk fuel. Biodesulphurisation is biologically possible and practically attainable at the laboratory scale. The development of microbial processes for removing organic sulphur from oils and coals is as yet unproven and is unlikely to be economic.