Diploma Thesis from the year 2007 in the subject Medicine - Human Genetics, grade: 1,0, University of Vienna (Institut fur Ernahrungswissenschaften), 96 entries in the bibliography, language: English, abstract: The aim of the present study was to investigate the effect of a triathlon (3.8 km swim, 180 km cycle, 42,2 km run) on the genomic stability of nine highly trained non- professional athletes. Therefore, the SCE assay, a relevant biological response marker for genotoxicity in human biomonitoring studies [PENDZICH et al., 1997] was performed using peripheral lymphocytes, on account of their effortless accessibility [WILKOSCY and RYNARD, 1990]. Duplicate lymphocyte cell cultures, of each participant, were incubated for 72 h (37 DegreesC, 5% CO2) according to a short-term human lymphocyte cell culture. For each participant at least 50 metaphases, containing 43-46 chromosomes were scored, to evaluate the mean SCE frequency. The number of SCEs per cell was calculated to a chromosome set of a normal diploid human cell, containing 46 chromosomes. In the present study the alteration of SCE frequency, 48 h pre- and 24 h postrace was evaluated. As an additional endpoint Top 5 HFCs (highest five absolute SCE means) were assayed. It could be demonstrated that both the total mean SCE frequency and the mean Top 5 HFC frequency (n=9) 24 h postrace were significantly decreased (*p