<p>This randomized controlled trial investigated the effects of 8-week chokeberry extract supplementation on nitric oxide (NO) metabolites, oxidative stress markers, inflammatory cytokines, and white blood cell (WBC) profiles in elite male rowers. Fifteen athletes received either chokeberry extract (<i>n</i> = 7; 3 × 200&#xa0;mg/day) or placebo (<i>n</i> = 8). A 2000-m rowing test was performed before and after supplementation, with blood collected pre-exercise, post-exercise, and 24&#xa0;h post-exercise. After supplementation, the chokeberry group showed higher plasma nitrite concentrations post-exercise (<i>p</i> = 0.0183, d = 1.95) and during recovery (<i>p</i> = 0.0034, d = 2.99), higher post-exercise nitrate levels (<i>p</i> = 0.0242, d = 1.45) as well as a higher total NOx (NO₂⁻ + NO₃⁻) post-exercise (<i>p</i> = 0.0114, d = 1.57) compared with placebo. Group differences were also observed in WBC subsets during the post-supplementation test, including lower lymphocytes post-exercise (<i>p</i> = 0.0075, d = 1.19), higher monocytes pre-exercise (<i>p</i> = 0.0128, d = 1.03) and post-exercise (<i>p</i> = 0.0086, d = 1.45), and higher granulocytes post-exercise (<i>p</i> = 0.0077, d = 1.40) in the supplemented group. No between-group effects were detected for TAOC, TBARS, IL-2, IL-10, or TNF-α. Additionally, after supplementation before exercise, IL-6 levels were higher in the supplemented group compared to the placebo group (<i>p</i> = 0.0407, d = 1.05). These findings indicate that chokeberry extract supplementation modifies NO-related biomarkers and selected immune parameters during exercise and recovery in elite rowers. The results demonstrate that chokeberry extract can influence physiological responses to intensive training in this athletic population.</p><p><b>Trial registration</b>: The study was registered on clinicaltrials.gov ID NCT06133751.</p>