We present in this paper results of a predictive code (SOCRATES: spacecraft/orbiter contamination representation accounting for transiently emitted species) which has been developed to assess the effects of contamination on measurements aboard spacecraft in low Earth orbit. SOCRATES is a Monte Carlo code which includes in its present version scattering, collisions leading to kinetic-to-vibrational energy transfer, and reactive collisions. The application of this code to actual measurements aboard spacecraft in low Earth orbit makes it possible to evaluate data obtained on these platforms with a view toward extracting the data of interest from contaminated signals. Molecules considered in the present study include CO2, H2O, OH, H2, and CO. ¿ American Geophysical Union 1990