Pure & Safe. Methylsulfonyl-Methane Biological Sulfur. Sulfur is the fourth most abundant mineral in the body. M-S-M (Methyl-Sulfonyl-Methane) is a naturally occurring sulfur-containing organic compound found primarily in fresh vegetables and fruits and in every cell of the body. M-S-M provides nutritional sulfur which is vital to the creation and regeneration of connective tissue.