A new technique for observing directly the absolute concentration of atoms and radicals in the earth's upper atmosphere is discussed. Atomic resonance fluorescence in conjunction with a parachute borne flow-through module deployed from a balloon at 40 kilometers is used to determine the ground state (3P) atomic oxygen concentration between 40 and 25 kilometers in the earth's atmosphere. Under daytime equilibrium conditions: 25 November 1974; 32¿N latitude; solar zenith angle 56¿, 10:30AM C.S.T., the absolute concentration of O(3P) is found to decrease from 1¿109 cm-3 at 39 km to 6¿107 cm-3 at 26 kilometers with statistically significant local structure evident in the altitude profile.