Atmospheric water vapor data derived from the special sensor microwave imager (SSM/I) are used to make time-coincident wet tropospheric range corrections to Geosate altimeter data in the Greenland-Iceland-Norwegian (GIN) Sea. The SSM/I sensor is onboard a polar orbiting Defense Meteorological Satellite Program platform and provides water vapor data at 25-km spatial resolution and an accuracy of 0.24 g cm-2. Water vapor height corrections were calculated and analyzed along all Geosat tracks crossing the area of interest in July and September 1987 and January and March 1988. Results indicate that the horizontal spatial variations in the altimeter height corrections can sometimes equal or exceed the magnitude (10--20 cm/100 km) of true GIN Sea sea surface height gradients, especially in the summer and autumn seasons. SSM/I and Geosat data must be closely matched in time, due to the potential rapid movement of atmopsheric systems through this region (35--40 km h-1). The water vapor data must be timely enough to adequately describe atmospheric conditions at the time of the altimeter pass, or significantly false signals may be introduced into the sea surface height data. Substantial differences in water vapor gradients were observed in SSM/I data sets 12 hours apart. Because of this, it is suggested that future satellite altimeter platforms include a nadir-viewing radiometer to provide time-coincident atmospheric water vapor data. ¿American Geophysical Union 1991