BACKGROUND: Oxygen uptake efficiency slope (OUES) is a method for investigating cardiorespiratory fitness and is proposed as an alternative to overcome the limitations of traditional measures such as peak oxygen consumption (VO(2peak)) for patients who do not achieve a maximum response, such as in Parkinson's disease (PD). OBJECTIVE: To assess the performance of individuals with PD during the six-minute walk test (6MWT) using the OUES. METHODS: This is an observational cross-sectional study including 12 individuals with PD and 12 healthy controls. Participants performed the 6MWT along with an analysis of exhaled gas kinetics. The OUES was determined from the last 16 s of the walk test. Multiple linear regression analyses were computed to explore associations between the independent (OUES) and the dependent variables (VO(2peak)) controlled by group. RESULTS: The OUES was associated to VO(2peak) on the 6MWT (β=0.24, p