An intense narrow intrusion of warm Gulf Stream water into the Sargasso Sea was detected by the NOAA 4 satellite in late April 1975. Analysis of satellite-derived sea surface temperature distribution and in situ data obtained within the intrusion indicated that the intrusion was a shallow zone (extending from the surface to about 200 m) of warm, less saline (in relation to the Sargasso Sea) Gulf Stream water about 95 km wide and extending 210 km in the north-south direction. The intrusion turned eastward in a cyclonic pattern, the southern portions extending another 150 km to the southeast. Southward flow was detected at the surface in the north-south portion of the intrusion with an average speed of approximately 1 m/s. The geostrophic computations suggested that the maximum depth of the zone of southward flow was about 200 m. Existing evidence suggested that the intrusion developed about April 9, 1975, following an intense coastal storm.