Detailed satellite observations of anticyclonic ring 81-D interacting with the Gulf Stream were collected as part of the August-September 1981 Warm Core Rings Experiment. Position of the ring centre, magnitude of the semimajor and semiminor axes and orientation are computed for 42 atmospherically corrected satellite images taken over a 2-month period in August, September and October 1981. Ring interaction with the Gulf Stream causes marked changes in shape, size, orientation and location of the ring. A longer history of 81-D is determined by using National Oceanic and Atmospheric Administration Gulf Stream analyses. Results of this analysis when compared with the precision estimates obtained above show good agreement in east-west location but relatively poorer correspondence in north-south position. Mean westward translation speeds are found for several rings to be ~0.05 m s-1. Steady westward translation is punctuated by periods of Gulf Stream interaction when a ring is observed to remain either stationary or propagate eastward with the mean Gulf Stream. Ring asymmetries of two types are noted. The first occurs when the ring is outside of the direct influence of the Gulf Stream. During these periods, the ring exhibits a spatially fixed or slowly counter- rotating mode, which is either D-shaped or elliptical. During interaction with the Gulf Stream, a more elliptical asymmetry, which rotates rapidly with the anticyclonic flow around the ring, is observed.