Individual Seasat altimeter profiles in the western North Atlantic have been differenced with the best available geoid model to remove the gravitational component. The resulting sea surface height profiles compare remarkably well with independent oceanographic observations. The Gulf Stream is clearly apparent in each profile as a 1- to 2-m step, and known positions of cyclonic and anticyclonic rings correspond with depressions and elevations, respectively, with amplitudes as large as 95 cm. Some of the most important altimeter data for analyzing the dynamic ocean signal were gathered during the last month of the mission when the same ground track was repeated every 3 days. These data allow detailed examination of time-varying ocean phenomena, since the gravitational component is time-invariant. One set of collinear passes clearly shows a cyclonic ring as it moves out from underneath the spacecraft's track, an event which was simultaneously observed with the aid of a satellite-tracked surface buoy. Another striking feature seen in the altimeter data set is the apparent variability exhibited by the Gulf Stream. On time scales of a few days, surface transport indicated by the sea surface height difference across the stream varied by nearly 30%, and over the entire 3-month period much larger fluctuations were observed, suggesting significant changes in total mass transport. Altimetry may provide an effective means of determining the time and space scales associated with these variations.