['"The aim of the study was to analyze exhaled breath condensate (EBC) proteome changes due to the effects of spaceflight factors. All the protocols were approved at the Institute of Biomedical Problems – Russian Federation State Scientific Research Center in the frame of Protocon experiment. EBC samples were collected by commercial devices RTube one month before flight (background) at the Yu. A. Gagarin Research and Test Cosmonaut Training Center, immediately after landing of the landing modules in the field (R0), and on the seventh day after landing as a part of medical examination (R+7). Semi-quantitative label-free proteomic analysis of 13 EBC samples collected from 5 Russian cosmonauts before and after long-term (169–199 days) spaceflights were performed and resulted in 164 different proteins. The highest number of proteins was detected in EBC after landing (R0). Pathways enrichment analysis via GO database large group of proteins that take part in keratinization processes (CASP14, DSG1, DSP, JUP, and etc). Nine proteins were KRT2, KRT9, KRT1, KRT10, KRT14, DCD, KRT6C, KRT6A, KRT5 were detected in all groups (background, R0, R+1). A two-sample Welch’s t-test identified the significant changing of KRT2 and KRT9 levels after landing. Enrichment analysis via KEGG database revealed significant participation (2,07E-06) of detected proteins in pathogenic E. coli infection (ACTG1, TUBA1C, TUBA4A, TUBB, TUBB8, YWHAZ). Presumably, presents of this proteins can associated with changing of cosmonauts’ microbial composition. Thus EBC can be used for noninvasive monitoring of health status and respiratory tract pathologies during the spaceflight. The obtained data are important for the development of medicine in extreme situations."']