A stress test has been designed which shows a consistent abnormality in platelets from carriers of the Wiskott-Aldrich-syndrome (W.A.S.) gene. 2-deoxy-D-glucose (D.D.G.), an inhibitor of glycolysis, completely inhibited second-wave adrenaline (epinephrine)-induced aggregation of platelets from 10 W.A.S. carriers, whereas it had no effect on the response of control platelets. Antimycin A (Ant A), an inhibitor of oxidative phosphorylation, had no effect on adrenaline-induced platelet aggregation of either carriers or controls. Incubation of control platelets with a combination of Ant A and D.D.G. inhibited aggregation in a way comparable to the effect of D.D.G. alone on carrier cells. Thus, W.A.S. carriers have a defect in platelet metabolism similar to that produced in normal platelets with Ant A. The D.D.G. stress test is a simple reproducible assay for detection of W.A.S. carriers.