Updated project metadata. This prospective study aimed to discover biomarkers in seminal plasma that could be employed for a non-invasive differential diagnosis of OA/NOA in order to rationalize surgery recommendations and improve success rates. Using label-free LC-MS/MS, we compared the proteomes of seminal plasma samples from fertile men (HC, n=8) and infertile men diagnosed with 1) OA (n=7), 2) NOA with successful sperm retrieval (mixed atrophy, n=8), and 3) NOA without sperm retrieval (Sertoli cell-only phenotype, n=7).