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Objective: Near-infrared spectroscopy (NIRS) is a noninvasive technique with the potential to determine the degree of tissue oxygenation. The aim of the current study was to investigate the use of NIRS as a reliable method of detecting calf muscle pump dysfunction in groups of patients with venous disease. Methods: Patients with superficial venous insufficiency (SW) or history of deep venous thrombosis (DVT) were classified according to the comprehensive classification system for chronic venous disorders (clinical class, etiology, anatomy, and pathophysiology) and compared with controls (GROUP variable). A 10-stage evaluation of ambulatory venous function was performed, and corresponding values of calf regional oxygen saturation (crSaO(2), %) at each phase were recorded (TIME variable). Thereafter, the percentage changes of crSaO(2) values (A scores, %) between a given phase and the reference phase were estimated. Differences among groups and phases were evaluated using analysis of variance. Subgroup analysis between C0-C2 and C3-C6 patients was performed. The receiver operating characteristic curve analysis was used to detect the best predictive capability for SW and DVT. Results: A total of 30 patients with SW, 31 patients with DVT, and 34 controls were included in the study. A statistically significant effect of TIME (F = 382.4; P < .001) and TIME x GROUP interaction (F = 6.3; P < .001) was recorded. Concerning prediction, we found a statistically significant area under the curve (AUC) for SW (AUC = 0.72; 95% confidence interval, 0.58-0.83; P = .003) and for DVT (AUC = 0.83; 95% confidence interval, 0.71-0.92; P < .0001) patients. Conclusions: The measurement of crSaO(2) using NIBS detected alterations in calf muscle pump oxygenation during exercise and differences in tissue oxygenation among SW patients, DVT patients, and controls. NIBS may represent a reliable noninvasive tool for the study of calf muscle dysfunction in venous disease and a useful vehicle for generating testable hypotheses in the laboratory setting.