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The aim of the study was to investigate the effect of retesting on the 12-min walking distance (12MWD) in patients with moderate or severe chronic obstructive pulmonary disease (COPD), with and without exercise-induced hypoxaemia (EIH) and to evaluate whether baseline characteristics derived before walking influence on variation of repeated tests. Fifty-seven COPD patients, mean age 66 (range 47 84) years, performed three 12-min walk tests within 1 week. Before and after each test, oxygen saturation (pulse oximetry, SpO 2), heart rate, breathing frequency, peak expiratory flow, and subjective ratings of exertion and dyspnoea were measured. EIH was defined as a fall in SpO 2 below 90% at the first walk test. The 12MWD did not increase on repeated testing in the EIH group. In the non-EIH group, the 12MWD increased by 12% (p<0.001) from test 1 to test 2 and by 4% (p<0.001) from test 2 to test 3. No day-to-day variation was observed in pre-walking characteristics. At least one training test is needed in non-EIH patients with COPD, as their effort and performance on the 12-min walk test increases on retesting (learning effects). In patients with EIH, the term "training test" is not relevant, as their walking distance did not homogeneously increase on repeated testing.