The endovascular treatment of intracranial aneurysms with detachable balloons requires filling materials that harden reliably and are compatible with the balloon. While the incompatibility of latex balloons and hema from different manufacturers is known, no incompatibility has been assumed thus far if both balloon and hema were from the same manufacturer. In two series of experiments, we filled a total of 20 latex balloons with hema as recommended by the balloon manufacturer. Within an observation time of 4 weeks all latex balloons ruptured. At the time of rupture, the balloons had gained 5-10% in weight, most likely due to osmotic shifts in water. Simultaneously, hardening of the hema resulted in a loss of elasticity of the latex. Until these compatibility problems are solved, silicone rather than latex balloons should be used with permanent filling materials such as hema for the endovascular treatment of intracranial aneurysms.