Heparin-associated thrombocytopenia (HAT) is a relative frequent complication of thromboembolic prophylaxis and therapy. There is good evidence that the more severe HAT Type II is caused by an anti body dependent on polysulfated oligosaccharide epitopes. At present, low molecular weight heparines are used with varying success in patients with HAT that require further anticoagulation, although there are several known eases of cross reactivity between standard and low molecular weight heparins. Using our present case as an example, we show that the in-vitro- diagnostic of cross- reactivity is an indispensable precondition for any sufficient therapy. Additionally, we give support to previous findings that the low-grade sulfated heparinoid Org 10172 showes no (or loss) cross reactivity with standard or low molecular weight heparins. Thus, it might be the most appropriate choice if an anticoagulation is necessary before the results of in-vitro-diagnostics are available.