Thermal infrared data from the NOAA polar orbiting satellite and hydrographic observations from surface ships are used to estimate the eccentricity and the rotation rate of wavelike perturbations around the circumference of a Gulf Stream cyclonic eddy in April 1977. From the satellite data, the rotation rate is estimated at ω = (4.4¿0.1)¿10-6 s-1 for the period April 8--16. Estimates of ω are obtained from the trajectory of satellite-tracked drifters and from changes in the sea surface temperature fields determined from expendable bathythermograph trace (XBT) surveys. A simple Eady model suggests the perturbations are stable modes of azimuthal wave number 2.