''Agathe,'' a joint Commissariat ¿ l'Energie Atomique (Saclay) and Centre d'Etude Spatiale des Rayonnements (Toulouse) experiment is a spark chamber for gamma ray measurements in the E>4 MeV energy range. It was used to measure the flux of atmospheric photons at &lgr;=-23¿ geographic latitudde (rigidity 11.7 GV) during two flights from Brazil, in the course of a campaign organized by the Centre National d'Etudes Spatiales, the French space agency. The results are compared to those obtained from flights of the engineering model of Agathe and a model for a time of flight system, tested to evaluate improvements for the Agathe experiment. The following results were obtained for the energy ranges 4--10 MeV, 10--25 MeV, and >25 MeV: (1) Determination of the atmospheric gamma ray fluxes or count rate as a function of pressure altitude; in these energy ranges the downward atmospheric flux is proportional to Pa with &agr;≂1. (2) The determination of the atmospheric spectrum at &lgr;=-23¿ in Brazil and at &lgr;=40¿ in the northern hemisphere; in Brazil the downward atmospheric spectrum can be represented by F(E)=2.4¿10-3 E-1.4 photons/cm2 s sr MeV g/cm2 in the 4- to 100-MeV energy range and F(E)=2.3¿10-2 E-1.9 photons/cm2 s sr MeV g/cm2 for E>100 MeV energy range. (3) The determination of the ratio between the fluxes measured in Brazil and in the norther hemisphere; this ratio is 1.8¿0.2. It has been shown that the fluxes of downward and upward moving gamma rays are equal at a pressure of about 40 mbar. The dependence of the downward moving fluxes as a function of the pressure is different from that published by Ling. But, if we assume that the atmospheric component is isotropic at 40 mbar, the experimental fluxes determined from the experiments described here agree with the measured fluxes taken into account by Ling in these calculations for the 4- to 10-MeV energy range. Key words: gamma radiation and atmospheric component.