The extensive use of mustard gas on the field caused the men to be exposed to low concentrations of the vapors for extended periods of time. Since it did not seem feasible to furnish the men with special fighting suits, which would protect them against these vapors, it was desirable to provide protection in the form of an ointment which could be applied to the body. In order to be satisfactory an ointment should have the following properties: (_a_) It should protect against saturated mustard gas during the longest possible exposure. (_b_) Its protective action should last as long as possible after the application of the ointment. It was felt that the ointment should give protection for 24 hours after it is applied, even if the body is perspiring freely. (_c_) The material should not be easily rubbed off under the clothing. (_d_) It should be non-irritating to the membranes of the body. (_e_) There should be no likelihood of toxic after-effects on long use. (_f_) It should be of a good consistency under a fairly wide temperature range and give a good coating at the temperature of the body. (_g_) Its method of manufacture should be simple and rapid, and the raw materials required should be abundant. (_h_) The cost should not be excessive. An extensive study of this question was made both in the laboratories and on the field. At first it was believed that successful results could be obtained by the use of such ointments. Careful investigation showed, however, that while these ointments really did protect against rather high concentrations of vapor for short times of exposure, they were probably not so valuable when used against low concentrations over an extended period of time. It was further demonstrated that the protection furnished by a coating of linseed oil is practically equal to the best ointment which has been developed. About 150 ointments were prepared and tested. These consisted of two parts or components, the metallic soap or other solid material and the oil or liquid part which bound and held the solid. The latter is called the base. The best base is lanolin, containing 30 per cent of water. A solution of wax in olive oil was next best. Of the metallic soaps the oleates and linoleates are better than the stearates. A satisfactory ointment has the following composition: Zinc oxide 40 Linseed oil (raw) 20 Lard 20 Lanolin 20 A modification of this formula is: Zinc oxide 45 Linseed oil 30 Lard 10 Lanolin 15