An ultrasonic nebulizer is of the type having a piezoelectric transducer communicating with a fluid reservoir and is characterized by having a protective cover of a predetermined wavelength which is superimposed on the transducer, an elastomeric boot in surrounding relation to the cover to prevent fluid loss from the interface between the cover and transducer, and an oil coupling medium is disposed in the interface for coupling the ultrasonic energy from the transducer to the cover.