Spaceborne measurements of tropospheric carbon monoxide (CO) were made by the Measurement of Air Pollution from Satellites (MAPS) experiment during April 9--19, 1994, and September 30 to October 11, 1994, from the space shuttle Endeavour. During the April mission, MAPS operated for 211 hours, with 736,471 s of nadir-viewing data, of which 161,619 s were cloud-free. In the October mission, MAPS operated for 256 hours, with 821,502 s of nadir-viewing data, of which 192,004 s were cloud-free. During the two 10-day Space Radar Laboratory flights, extensive and internally consistent correlative measurements and observations were made on the ground at nearly 30 sites between 70 ¿N and 67 ¿S, from five aircraft in three countries, and by the astronaut crews from the space shuttle. These ancillary measurements provided critical information on the nature of the atmospheric environment during the flights, the distribution of the CO mixing ratios in the boundary layer and in the middle troposphere, and the vertical distribution of CO at some locations. Although the airborne CO measurements are the key validation data sets for the MAPS measurements, the ground-based CO measurements provide a near-surface CO boundary condition for modeling applications and for CO emissions investigations. This paper will present the measurements of the April and October 1994 and the October 1984 MAPS CO data. These MAPS results compare well (¿10%) with the intercalibrated airborne measurements from the NASA DC-8 flights over North America, and CO profiles from the Commonwealth Scientific and Industrial Research Organization aircraft near Cape Grim, Tasmania. Longitudinal and latitudinal transects of the MAPS CO measurements show significant seasonal variability consistent with the seasonal shifts in the locations and strengths of the CO sources. In April the highest average CO values (~120 ppbv, averaged throughout the depth of the atmosphere) are found over the high northern latitudes, with decreasing amounts (~45 to 60 ppbv) toward the southern middle and high latitudes. The CO distribution changed dramatically by October with the CO gradient being reversed from that measured during April. During October the highest CO values (greater than 135 ppbv) are concentrated in a tropical envelope extending over central South America, southern Africa, southern India, Indonesia, and northern Australia. Numerous and extensive fires in these areas were observed and photographed by the STS 68 astronaut flight crew. ¿ 1999 American Geophysical Union