THE mechanism of elemental sulphur transport from the medium into the cells of sulphur-utilizing micro-organisms was investigated by Umbreit, Vogel and Vogler1, They concluded that for Thiobacillus thiooxidans, the sulphur, on contact with the cells, dissolves in globules of highly unsaturated fat located at the poles of the cells. Knaysi2 was unable to confirm the existence of polar fat globules and pointed out the difficulties involved in postulating contact between an extracellular particle and an intraprotoplasmic structure. Vishniac and Santer3 suggested a sulphur-transport mechanism involving reduced glutathione (GSH) or a similar molecule reacting as follows: the sulphide formed enters the cell in free or bound form and the GSSG is reduced by subsequent intracellular sulphide oxidation. No experimental evidence was presented to support this mechanism. It is apparent that the problem is not yet solved.