A balloon catheter device (1400) for delivering a substance to an ostium of a paranasal sinus of a human or animal subject, said device comprising: a catheter shaft (1402) having a balloon inflation lumen； a balloon (1404) attached to the catheter shaft (1402) and in fluid communication with said balloon inflation lumen (1410)； and characterized in that said device further comprises a porous outer sheath (1406) attached to the catheter shaft (1402) and surrounding the balloon, an agent delivery lumen (1412) in said catheter shaft (1402) in fluid communication with a region between the balloon (1404) and the porous sheath (1406), the balloon being inflatable for compressing the porous outer sheath (1406) against tissue within said paranasal ostium whereby a therapeutically effective amount of the substance introduced through said agent delivery lumen can pass through the porous outer sheath and into contact with the paranasal ostium.
