A nasal delivery device for and a method of delivering a substance to a nasal cavity of a subject, the delivery device comprising: a delivery unit for delivering a flow entraining a substance to one nostril of a subject, the delivery unit including a nosepiece for fitting to a nostril of the subject and a flow resistor unit for fitting to the other nostril of the subject, the flow resistor unit including a progressive resistor for progressively providing an increasing flow resistance to the delivered flow.
