a humidity control system for a musical instrument case includes at least two compartments venting into the inside of the case . at least one of these compartments is fitted for a desiccant pouch , with at least one compartment alternatively used and fitted for a humidifier . the use of more than two compartments may be occasioned by an extreme local atmosphere or an exceptionally large instrument or both . a hygrometer and a thermometer are preferably provided with the case to enable a musician to easily ascertain the environmental conditions inside the case . the musician then adds either the desiccant pouch or activates the humidifier in the appropriate compartment of the carrying case , as necessary . the compartments can be built into the case or fastened using conventional fasteners such as adhesive or snaps .