Abstract Spin-spin correlation parameters A LL , A NN , A SS , A SL and spin asymmetries A NO and A ON have been measured for the reaction p p → pn π + with incident beam energies of 510, 465 and 420 MeV. Clean separation of free proton events from the bound proton background has been achieved. A LL , A SS and A NN , were all found to be large and negative indicating domination by the 1 D 2 partial wave. The spin asymmetries were large. Results are compared to the predictions of Dubach, Kloet and Silbar.