At Pinjarra and Bakers Hill, Western Australia, the rate of breakdown of elemental sulphur applied in different size gradings was followed over two seasons by periodically measuring the elemental sulphur remaining in the soil. Similar measurements were made on experiments at Kwolyin, Darkan, and Pinjarra in which commercial sulphur fertilizer was applied in the autumn of two successive years. Particles finer than about 200 mesh oxidized quickly and would be a poor source of slowly available sulphur. Particles between 40 and 100 mesh appeared to provide the best compromise between too fast and too slow oxidation. Oxidation appeared to be faster at sites with higher annual rainfall and faster in the second year of application than the first. The commercial sulphur fertilizer was an effective source of slowly available sulphur and produced pasture responses at all three sites in the first year. Responses continued into the second year but the level of effectiveness relative to a current dressing could, not be accurately measured. At the Pinjarra site, two annual applications produced a 2.5-fold increase in yield of clover. A total of 19 soils were tested in incubation experiments for their ability to oxidize sulphur. All soils were able to do this and differences between soils were small when small amounts of sulphur were used. Differences between soils were larger when large amounts of sulphur were used.