A system for treating a disease or disorder of the ear, nose or throat of a human or animal subject, said system comprising: a guide catheter (40a-40f) that is insertable through a nostril of the subject, said guide catheter (40a-40f) having a substantially rigid shaft, a proximal opening, a distal opening and a lumen extending between the proximal opening and the distal opening; a working catheter that is insertable through the lumen of the guide catheter (40a-40f), said working catheter having a guidewire lumen, a substantially rigid proximal portion and a distal portion that is more flexible than the proximal portion; a guidewire that is advanceable through the guidewire lumen; and a member that is attachable to the guidewire and limits the extent to which the guidewire is advanceable through the working catheter, wherein the member is configured such that the guidewire may be advanced until the member frictionally engages a hub on the working catheter, said engagement of the member with the working catheter being operative to hold the guidewire in a substantially fixed position relative to the working catheter; the distal portion of the working catheter being advanceable out of the distal opening of the guide catheter and having a working element that is useable to perform a desired diagnostic or therapeutic task at a location within the ear, nose or throat of the subject; the working catheter being sized relative to the guide catheter (40a-40f) so that, when the distal portion of the working catheter is advanced out of the distal opening of the guide catheter (40a-40f) and the working element is being used to perform the desired diagnostic or therapeutic task, only the substantially rigid proximal portion or some portion thereof will extend out of the proximal opening of the guide catheter (40a-40f). a guide catheter (40a-40f) that is insertable through a nostril of the subject, said guide catheter (40a-40f) having a substantially rigid shaft, a proximal opening, a distal opening and a lumen extending between the proximal opening and the distal opening; a working catheter that is insertable through the lumen of the guide catheter (40a-40f), said working catheter having a guidewire lumen, a substantially rigid proximal portion and a distal portion that is more flexible than the proximal portion; a guidewire that is advanceable through the guidewire lumen; and a member that is attachable to the guidewire and limits the extent to which the guidewire is advanceable through the working catheter, wherein the member is configured such that the guidewire may be advanced until the member frictionally engages a hub on the working catheter, said engagement of the member with the working catheter being operative to hold the guidewire in a substantially fixed position relative to the working catheter; the distal portion of the working catheter being advanceable out of the distal opening of the guide catheter and having a working element that is useable to perform a desired diagnostic or therapeutic task at a location within the ear, nose or throat of the subject; the working catheter being sized relative to the guide catheter (40a-40f) so that, when the distal portion of the working catheter is advanced out of the distal opening of the guide catheter (40a-40f) and the working element is being used to perform the desired diagnostic or therapeutic task, only the substantially rigid proximal portion or some portion thereof will extend out of the proximal opening of the guide catheter (40a-40f).