The quenching rate k7 of the O(1D) by O(3P) in the nocturnal F region is evaluated on the basis of rocket-borne photometric and electron density measurements that have been carried out aboard a Brazilian Sonda III rocket launched from Natal (geography 5.8¿S, 35.2¿W) on October 31, 1986, at 2259 Local Standard Time (LST). The nightglow emission and electron density vertical profiles were obtained respectively from a 630-nm photometer and a high-frequency capacitance probe. The quenching rate k7 was evaluated from model calculations of the OI 630-nm emission rate, utilizing as input data the measured electron density. Assuming the value of 1.1 for the quantum yield factor f(1D) a mean value estimated for k7 turned out to be 9.2¿10-13 cm3 s-1, the upper and lower limits being 2.8¿10-12 cm3 s-1 and zero, respectively. On the other hand, assuming Bates' [1990> height profile of Franck--Condon f(1D) for this same experiment, k7 resulted in 2.55¿10-12 cm3 s-1. These results are discussed and compared with previous measurements from other authors. ¿ American Geophysical Union 1993