An oscillatory positive expiratory pressure therapy device, comprising: an air-flow tube having a path of air flow movement from an inlet opening for receiving expiratory air passed thereto by a user receiving respiratory therapy, through an outlet opening for discharging the expiratory air passed through said inlet opening; said air-flow tube including expiratory air responsive closure means positioned in said path of air flow movement and actuable between an open position and a closed position in response to the pressure of expiratory air passed thereto; said expiratory air responsive closure means including a normally closed non-linear discharge outlet which is opened in response to the presence of a predetermined pressure of expiratory air being passed in said path of air flow movement, and which closes in response to a predetermined rate of air pressure decrease through said non-linear discharge outlet; said expiratory air responsive closure means further including a closure member movable in response to expiratory air in said path of air flow movement between a closed position blocking the flow of expiratory air and an open position permitting the flow of expiratory air in said path of air flow movement; the air-flow tube having at one end opposite the inlet opening an inspiratory inlet air port through which inspiratory air is drawn into the device to be received by the patient; wherein the device further comprises nebulizer coupling means connected to the air-flow tube 200 for connecting a nebulizer into fluid communication with an inspiratory air-flow path from the inspiratory inlet air port to a user; wherein the device further comprises a one-way valve positioned downstream of the inspiratory inlet air port and the nebulizer coupling means so that inspiratory air may freely enter the device through the one-way valve, but expiratory air from the patient is blocked from being expelled through the inspiratory inlet air port or through the nebulizer coupling means. an air-flow tube having a path of air flow movement from an inlet opening for receiving expiratory air passed thereto by a user receiving respiratory therapy, through an outlet opening for discharging the expiratory air passed through said inlet opening; said air-flow tube including expiratory air responsive closure means positioned in said path of air flow movement and actuable between an open position and a closed position in response to the pressure of expiratory air passed thereto; said expiratory air responsive closure means including a normally closed non-linear discharge outlet which is opened in response to the presence of a predetermined pressure of expiratory air being passed in said path of air flow movement, and which closes in response to a predetermined rate of air pressure decrease through said non-linear discharge outlet; said expiratory air responsive closure means further including a closure member movable in response to expiratory air in said path of air flow movement between a closed position blocking the flow of expiratory air and an open position permitting the flow of expiratory air in said path of air flow movement; the air-flow tube having at one end opposite the inlet opening an inspiratory inlet air port through which inspiratory air is drawn into the device to be received by the patient; wherein the device further comprises nebulizer coupling means connected to the air-flow tube 200 for connecting a nebulizer into fluid communication with an inspiratory air-flow path from the inspiratory inlet air port to a user; wherein the device further comprises a one-way valve positioned downstream of the inspiratory inlet air port and the nebulizer coupling means so that inspiratory air may freely enter the device through the one-way valve, but expiratory air from the patient is blocked from being expelled through the inspiratory inlet air port or through the nebulizer coupling means.