update modification list This work was aimed at estimating the concentrations of proteins encoded by human<BR><BR> chromosome 18 (Chr 18) in blood plasma of 54 healthy male volunteers. These young male persons are certified by the medical evaluation board as healthy subjects ready to space flight training. Over 260 stable isotope-labeled peptide standard (SIS) as well as corresponding non-labeled proteotypic peptides were synthesized to perform the measurements of the proteins encoded by Chr 18. Selected reaction monitoring (SRM) with SIS allowed to estimate the levels of 84 out of the 276 proteins encoded by Chr 18 in the samples from 54 donors.