Background. Chronic fatigue syndrome (CFS) patients often complain that they are more susceptible to acute mental fatigue. It is important to determine whether this is observed using objective tests of sustained attention and responding.

Methods. Sixty-seven patients who fulfilled the criteria for CFS proposed by Sharpe et al. (1991) were compared with 126 matched healthy controls. Acute fatigue was assessed by comparing performance at the start and end of a lengthy test session and by examining changes over the course of individual tasks.

Results. CFS patients showed impaired performance compared to the controls and these differences increased as the volunteers developed acute fatigue. In addition, differences between the two groups were larger at the end of the test session.

Conclusions. The present results show that CFS patients are more susceptible to acute fatigue than healthy controls. This could reflect motor fatigue or an inability to compensate for fatigue with increased effort. This profile is consistent with previous research on fatigue and suggests that interpretation of certain aspects of CFS may be helped by considering it as the end point of a continuum of fatigue rather than a distinct disease.