Abstract: Schelling, X, Calleja-González, J, Torres-Ronda, L, and Terrados, N. Using testosterone and cortisol as biomarker for training individualization in elite basketball. A 4-year follow-up study. J Strength Cond Res 29(2): 368–378, 2015—The purpose of this study was to determine the responses of testosterone and cortisol, with special reference to playing positions, playing time (PT), and phase of the season. We performed a follow-up study during 4 consecutive seasons to investigate the effects of PT, positional role, and phase of the season on anabolic-catabolic biomarkers (plasma total testosterone -TT- and cortisol -C-) on 20 professional male basketball players (27.0 ± 4.2 years; 24.4 ± 1.2 kg·m−2). First blood samples were collected right after the off-season period and considered as baseline. Samples were taken periodically every 4–6 weeks, always after a 24- to 36-hour break after the last game played. Statistical procedures were nonparametric mainly. Hormonal status was playing position-dependent, power forward (PF) showed the lowest TT values (median ± interquartile range [IQR]; PF: 18.1 ± 4.9; nmol·L−1), and small forwards showed the highest ones of cortisol (0.55 ± 0.118 μmol·L−1). Players who played between 13 and 25 minutes per game showed the highest values of TT (22.8 ± 6.9 nmol·L−1) and TT/C (47.1 ± 21.2). March and April showed the most catabolic or stressed hormonal state (low TT/C values and high ones of cortisol) and that is necessary to take into account according to PT (>25-minute per game) and specific playing position. Monitoring plasma TT and cortisol is recommended to prevent excessive stress caused by professional basketball season requirements.