Synthetic hosts are to transport medical substances into the body and to release them at specific points. They enclose the active substances in a cavity. In case of steroids, this task has been accomplished mainly by ring-shaped glucose molecules so far. Now, scientists have discovered a new class of host molecules, namely, barrel-shaped cucurbiturils. They can make hardly soluble steroids, such as cortisone or estradiol, act more gently and more efficiently.