Neutral hydrogen observations of the interacting galaxies NGC 4725 and NGC 4747.

New high sensitivity single dish and aperture synthesis H I observations are presented of the galaxies NGC 4725 and NGC 4747. The kinematics and distribution of H I in the two galaxies strongly suggest that they are tidally interacting. A 45 - 50 kpc long H I plume extends from the centre of the small peculiar galaxy NGC 4747 but is offset in position angle by 11° from an associated optical plume. To the south of the galaxy a weaker clumpy H I plume is observed which points back towards NGC 4725. This plume has a small velocity gradient along its length which is in the opposite sense to that of the main rotation of the galaxy. The giant spiral galaxy NGC 4725 is dominated in H I by a main outer arm. Evidence is presented which shows that the arm is probably warped out of the plane of the galaxy. A number of other inner spiral arms and an inner H I ring are discussed.