Background <p>Baseball pitchers repeatedly throw at full strength, leading to pathological changes in the brachial artery, which can cause symptoms such as hand numbness and arm fatigue, potentially resulting in decreased performance. Decreased brachial artery endothelial function might serve as an early sign of these changes.</p> Aims <p>This cross-sectional study aimed to compare brachial artery endothelial function between the throwing and non-throwing arms of baseball pitchers, as an initial step toward understanding whether endothelial dysfunction contributes to pathological changes and symptoms in the brachial artery.</p> Methods <p>A total of 30 male baseball pitchers (mean age: 20 ± 1&#xa0;years) participated in this study. We measured the flow-mediated dilation (FMD) as an indicator of brachial artery endothelial function using an ultrasound diagnostic device.</p> Results <p>Brachial artery FMD was significantly lower in the throwing arm than in the non-throwing arm (6.8% ± 3.3% vs. 5.4% ± 2.4%, <i>P</i> = 0.01). In contrast, the throwing arm had a higher baseline brachial artery diameter than the non-throwing arm (4.1 ± 0.5&#xa0;mm vs. 4.3 ± 0.4&#xa0;mm, <i>P</i> = 0.01). After adjusting for the difference in the baseline brachial artery diameter, the FMD of the throwing arm tended to be lower compared to the non-throwing arm (<i>P</i> = 0.08).</p> Conclusions <p>Brachial artery endothelial function may be reduced in the throwing arm compared to the non-throwing arm. This difference could represent an early sign of pathological changes in the brachial artery of baseball pitchers and may serve as a potential target for diagnosis or treatment.</p> Graphical abstract <p></p>