The proton-proton and proton-neutron elastic-scattering angular distributions have been measured at 1.69 GeV/c (=991 MeV) from 14.5° to 150° c.m.s. using fast scintillation counters in conjunction with magnetic-momentum analysis. In both cases, the forward elastic cross-sections are considerably in excess of their respective optical-theorem minima, the results being consistent with the existence of a real part in theT=0 scattering amplitude together with spin dependence in both interactions. The proton-neutron angular distribution is more strongly asymmetric about 90° c.m.s. than it is at lower energies, indicating the onset of diffraction scattering and increased interference between the scattering amplitudes in theT=0 andT=1I-spin states. At the larger centre-of-mass angles, the data suggested that substantial corrections were necessary because of the inapplicability of the impulse approximation as a result of multiple nuclear scattering in the deuteron, necessitating a measurement of the ratio of quasi-elastic to elastic proton-proton scattering from 100° to 150° c.m.s.