Together with Prof. Henning Sirringhaus and his colleagues at the University of Cambridge we have studied the influence of electron spins on the electrical transport in field-effect transistors (FETs) based on organic semiconductors. Using Electrically Detected Magnetic Resonance (EDMR) measurements performed on ambipolar FETs we could show that the choice of the transport regime strongly influences the type of the dominating spin-dependet transport processes. The results of our study will soon be published in Physical Review Letters.