GPX1 and Infertility: The present observational case–control study aimed to examine seminal plasma concentrations of prostaglandin E2 (PGE2), 6-keto-prostaglandin F1α (6-keto-PGF1α), F2-isoprostane, superoxide dismutase 1 (SOD1), glutathione peroxidase 1 (GPX1), nitric oxide synthase 1 (NOS1), and their ratios, in fertile (n = 22, aged 24–45) and infertile (n = 250, aged 21–47) men, including analyses across specific infertile subgroups, using ELISA assays.