Improved modeling of the earth's geopotential is one of the major tasks of satellite geodesy. The availability of a new set of precise LAGEOS satellite laser ranging (SLR) data as well as Seasat-acquired observations enabled us to compute an improved solution in the GRIM model series. The new geopotential GRIM3-L1 recombined the satellite perturbation normals of the former GRIM3 solution with new normal equation subsystems derived from an additional 16 months of LAGEOS SLR data, oceanic 1¿¿1¿ mean free air anomalies recovered from Seasat altimetry, an updated set of terrestrial 1¿¿1¿ mean free air anomalies, and severa condition equations for zonal and resonant harmonics. The combined normal equations were solved for a complete set of spherical harmonics up to degree and order 36 and the coordinates of 109 tracking stations. Comparisons with altimetry-derived quantities, terrestrial gravity, anomalies from satellite-to-sattelite tracking, longitude accelerations of 24-hour satellites, and sattelite orbit fits show a substantial improvement over previous GRIM solutions and indicate that the LAGEOS data have contributed considerably to the reliable estimation of the long-wavelength portion of the gravity field.