Abstract: An antisepticizing device comprises a cap having a formation adapted to fit complementarily with the end fitting of the catheter and formed with a passage having one end communicating with the end fitting and therethrough with the catheter when the end fitting is fitted to the formation. A reservoir in the cap has a movable wall, and the other end of the passage opens into the reservoir which contains a body of an antiseptic liquid. The movable wall of the reservoir can be displaced to force the liquid through the passage into the catheter fitted to the formation. This movable wall can be formed as a piston slidable in the reservoir and having the formation and passage. The end fitting and cap have complementary screwthreads.