In this paper, we present and analyse various aspects of the leak of toxic gas from the Union Carbide Plant at Bhopal, India in December 1984. The physicochemical properties of the deadly methyl isocyanate (MIC) and its biological activity, as well as the probable causes of the accident, are discussed. The role of meteorology and topography with regard to the dispersion process is also documented. To obtain an estimate of the possible concentration levels of MIC in the atmosphere, an analytic dispersion model has been formulated. The model output gives an estimate of the ground level concentration and the approximate time of arrival of the plume front in the various affected localities. Dry deposition and the aqueous phase conversion of MIC with the humid atmosphere were also featured in the model. The model results seem to be fairly well correlated with the scantily available mortality distribution records. Finally, the paper ends with descriptions of the disastrous effect of the gas on animals, plants and humans. © 1987.