The external beam of 51.5 MeV deuterons from the Karlsruhe isochronous cyclotron was used to investigate the three particle reactions p(d,pp)n and d(d, dp)n. A kinematically complete experiment was performed by detecting the two emitted protons respectively the proton and the deuteron in coincidence. The data for the reaction p (d, pp) n exhibit a pronounced final state interaction between the outgoing neutron and one proton. This final state interaction is mainly due to the n- p singlet interaction and the extracted n- p scattering length is |as|=(19±2.5) fm. In the investigation of the reaction d(d, dp)n the angles were chosen as to observe quasielastic deuteron-proton-scattering predominantly. The data was analysed in terms of the Chew Low Spectator model and we obtained by on-energy-shell" extrapolation for the d-p cross section the value (7±2.5) [mb/sr]. This value has to be compared with the cross section for free d-p scattering which was independently measured and the value obtained for the corresponding angle is (16±1) [mb/sr]. © 1969 Springer-Verlag."