When DMSO is added to culture medium to freeze eukaryotic cell lines, and the cells are thawed, DMSO must be removed within a few hours or the cells will die. Although DMSO helps stabilize cells during freezing, it does have toxicity, so the amount of time it is left in contact is important, as well as the concentration as noted in the last comment.
Damso cannot be used to research microbial activities since it is thought to be lethal to it. Many studies suggest using 10 microliters of it in addition to 990 milliliters of distilled water to produce 1 ml.