Based on animal results and as regards shortterm administration of dimethyl sulfoxide (DMSO) clinically, repetitious and detailed ophthalmoscopic rechecking of patients seems unnecessary. However, when long-term administration is contemplated, exacting pretreatment study is necessary in order that lenticular abnormalities or other pathologic ocular conditions already present may be identified and quantitated. Only with such base-line information can the possible undesired effects of medication be objectively followed. if any single fact has emerged from animal and human studies with DMSO to date, it is that the lens toxicity findings originally reported in dogs and later confirmed in certain other species have no equivalent or counterpart in human therapy utilizing DMSO in generally accepted regimens.