Summary. Aperture-synthesis observations of neutral hydrogen in M33 at large distances from the nucleus are described. The angular resolution is 7 x 15 arcmin, and the velocity resolution is 16 km/s. The H i `wings' are detected to a distance of 70 arcmin (14 kpc) from the nucleus, both to the SE and NW, with radial velocities deviating from normal rotation by up to 70 km/s. The distortions are interpreted as warping of the plane, and a simple model for the H I distribution reproduces well the large-scale features of the perturbation. Much larger extensions in R and z are required than in the model by Rogstad, Wright & Lockhart, and a slower trend of inclination and position angle with radius.