Abstract : Diver's breathing gas hoses manufactured according to a detailed military specification (MILH2815G, 17 Feb 1989) are used throughout the U.S. Navy. MIL-H-2815G details specific chemical offgassing requirements that the manufacturer of these hoses must meet. However, the U.S. Navy does not presently require a specific set of cleaning and/or testing procedures to be done by the user to insure that these hoses will not introduce potentially harmful chemicals into the breathing gas. Recent experience at the Naval Medical Research Institute (NMRI) suggests the need to clarify how such hoses should be treated (i.e., when and how cleaning and chemical testing should be done). Limited chemical testing by NMRI indicated that at least some of the hoses introduced varying amounts of several contaminants into the gas, the predominant species being toluene, a common aromatic hydrocarbon. Although we are unaware of any recent health or safety problems that can be attributed to chemical properties of diving hoses, this record of apparent safe use should not be used to minimize concern regarding hose safety.