The apparatus includes a ureter occlusion apparatus, which comprises, in combination: at least one longitudinally extending plug body (26) of flexible, physiologically acceptable material which obstructs the passage of all particulate matter great than 5 microns in diameter, is laterally compressible to a compressed diameter of not more that 2 millimetres and is laterally expandable in the presence of liquid to an external diameter of at least 1.0 centimetre, a physiologically acceptable flexible guide sheath (21) dimensioned for removable insertion into the ureter, the guide sheath having an internal diameter for receiving the plug body in compressed dry form and being retractable around the plug body so as to leave the plug body in position in the ureter and a removable physiologically acceptable stylet (22) and guide wire (20) which together allow positioning of the guide sheath within the ureter with both the guide wire and stylet being subsequently removable from the guide sheath to allow the plug body to be installed in the ureter via the guide sheath.
