We measured in thermal emission the 63-μm line due to thermospheric atomic oxygen O(3P), using a far-infrared spectrometer on a balloon platform at 37 km altitude over Palestine, Texas (32¿N), on June 20, 1983. From measurements of the equivalent width of this line at two elevation angles, we find a weak angular dependence: the equivalent width increases by a factor of 1.5¿0.3 as the angle decreases from +30¿ to +1¿. Since the optical depth of the O(3P) line is large, we cannot directly convert the measured line intensity to a column abundance. lnstead, we interpret the measurements in terms of radiative transfer through a 16-layer atmosphere extending to 200 km. We use a model atmosphere for summer at 30¿N, with an exospheric temperature of 1300 K, including (1) an assumed daytime atomic oxygen abundance profile constructed from recent chemical and dynamical models and (2) a water vapor abundance profile constructed from recent experimental and model results. For this assumed O(3P) vertical profile shape we determine from our spectra at two elevation angles a multiplicative scaling factor of 0.8, with an altitude-dependent uncertainty. In the best-determined layer the uncertainty in the multiplier is ¿0.2 at 119 km. The model-dependent peak atomic oxygen density is 3.6 (¿1.9)¿1011 cm-3 at an altitude of about 101 km. ¿American Geophysical Union 1987