Guidelines for conducting the 6-minute walk test (6MWT) indicate that oxyhaemoglobin saturation (SpO( 2)) should not be monitored constantly during the test. The aim of this study was to determine whether the nadir SpO(2) differs from the end-6MWT SpO(2) in patients with chronic respiratory disease. A total of 86 subjects underwent the 6MWT according to a standardized protocol with continuous monitoring of SpO(2) by pulse oximeter. Comparison of nadir SpO(2) and end SpO(2) was made and the proportion of subjects with important desaturation according to each measure was determined. The effect of resting during the 6MWT on the likelihood of a significant difference between nadir and end SpO(2) was evaluated. A total of 29 subjects with chronic obstructive pulmonary disease (COPD; mean [SD] forced expiratory volume in 1 second [FEV(1)] 51 % predicted) and 57 with interstitial lung disease (ILD; TLCO 49 % predicted) were studied. Nadir SpO(2) was slightly lower than end-test SpO(2) (median 87% vs. 88%, p < 0.001) with differences ranging from 1% to 10%. Those who rested during the test (n = 14) were more likely to have a significant difference between nadir SpO(2) and end SpO(2) (p = 0.04). End SpO(2) did not accurately identify desaturation in 21% of subjects. No differences between COPD and ILD were observed. For most patients with chronic respiratory disease, the end SpO(2) and the nadir SpO( 2) are similar during the 6MWT. However, the end SpO(2) does not give an accurate estimate of nadir SpO(2) in patients who rest. Consideration should be given to the constant monitoring of SpO(2) during the 6MWT.