GPx activity represents the second line of enzymatic antioxidant defense, and Gpx1, one of six isoforms of GPx, is widely present in human cells and in vascular endothelium too . The GPx1 rs1800668 (C>T) polymorphism has been reported to affect GPx1 gene transcription rate and could reasonably play a role in increased individual susceptibility to oxidative stress. Water polo players having the T mutated allele had pre- and postexercise increased levels of prooxidant markers (dROMs, AOPP) and decreased levels of antioxidant markers (BAP, thiols), even if significant differences were only found for dROMS after exercise, likely due to the small size of genotype subgroups. Our preliminary results suggest that the GPx1 rs1800668 polymorphism plays a major role in modulating antioxidant enzyme activities, since both SOD and CAT activities were significantly increased in heterozygous CT water polo players compared with wild-type subjects. Instead, this GPx1 polymorphism seems to play a minor role in muscle damage given that although water polo players having the CT heterozygous genotype showed the highest levels of LDH, CK, and myoglobin after exercise, these differences were not statistically significant in comparison with wild-type subjects.