This study compared the hemorheological profile at rest and in response to a short supramaximal exercise test between sickle cell trait (SCT) carriers and a control group. Eight SCT carriers and eight control subjects performed a ramp exercise test on a cycle ergometer conducted to maximal oxygen uptake ðV_ O2maxÞ: One week later, they performed a supramaximal exercise test consisting of pedaling for 1 min at 110% V_ O2max: Blood viscosity (gb), plasma viscosity (gp), hematocrit (Hct) and red blood cell (RBC) rigidity were assessed at rest, at the end of exercise and at the 15th, 30th and 60th min of recovery. Exercise increased gb, gp and Hct above resting values in both groups and these parameters remained higher until the 15th or 30th min of recovery as compared to resting values. RBC rigidity was unchanged from baseline values in both groups during exercise and recovery. No difference was observed between the two groups for gp and Hct but gb and RBC rigidity were higher in the SCT carriers at every time point compared with the control group. The higher RBC rigidity and gb found in SCT carriers at rest and in response to a brief supramaximal exercise might constitute a risk factor for microcirculatory complications. Indeed, a short supramaximal exercise test may not be completely inoffensive for SCT carriers.