ATOMIC-HYDROGEN IN THE SPIRAL GALAXY NGC-3631

New high-resolution, high-sensitivity Westerbork Synthesis Radio Teles cope H I synthesis observations of the spiral galaxy NGC 3631 are pres ented. In the total atomic hydrogen map, the spiral arms are well dist inguished from the interarm regions, while the sensitivity allows dete ction of H I in all but a few isolated regions of the areas between th e spiral arms. Most of the atomic hydrogen is located within the optic al disc, but the H I extends to some 1.5R(opt). The H I follows the sp iral arms, and streaming motions of up to similar to 15 km s(-1) (proj ected) can be identified from the velocity field. Assuming a constant inclination angle of 17 degrees, a rotation curve is derived which is declining slightly in the outer parts of the disc. An analysis of a re sidual velocity field, obtained after the subtraction of an axisymmetr ic model based on the rotation curve, confirms the existence of stream ing motions near the spiral arms in an otherwise undisturbed disc.