The observation of infrared absorption lines by means of a grille spectrometer on board Spacelab 1 allows the determination of Co2 and CO in the low thermosphere and in the middle atmosphere. Equal abundances of CO and CO2 are found at 115 ± 5 km altitude. CO2 is observed to depart from its homospheric volume mixing ratio near 100 km, dropping by a factor of 10,15 km higher. The CO largest number density is observed near 70 km altitude, close to the H Lyman alpha photoproduction peak. The analysis of one run dedicated to the observation of water vapor shows a middle atmospheric mixing ratio of this species within the limits : 3 to 8 ppmv up to 70 km altitude, with the indication of an increase from 30 to 50 km altitude. The H2O mixing ratio drops very rapidly above 70 km. The comparison of the results from strong and weak H2O and CO2 lines shows the need to refine the line profile model.