Besides personal experience as a former research fellow, the prerequisites for a successful research fellowship in the USA were analysed. Individual initiatives without any infrastructure for successful reintegration at home will fail. Isolated publications will carry the insignia of the guest university without providing benefit for the home institution at a later stage. The ideal constellation is the continuity of international cooperation in combination with an active research group at home. In addition to the respective publications, the following achievements of a research period in the USA can be attained: Establishing ongoing contacts to an international research group in the own field of interest; training in "how to write a scientific paper"; introduction to the "international scientific community". The potential contact to other groups cannot be planned, but represents an important aspect of a research period. To learn to appreciate other peoples' way of living adds to the personality of every scientist.