  We compare different formalisms for the calculation of lepton pair emission
in hadron-hadron collisions and discuss the consequences of the approximations
inherent to each of them. Using a Lorentz-covariant and gauge-invariant
formalism proposed by Lichard, we calculate lepton pair emission via
bremsstrahlung in proton-proton and neutron-proton reactions at energies
between 1 and 5 GeV to leading order in the virtual photon four-momentum. These
new results suggest that some previous bremsstrahlung calculations based on
varieties of the soft-photon approximation might have somewhat overestimated
the DLS low-mass dilepton cross sections. We find that the respective
intensities of dilepton production through $p p$ and $n p$ bremsstrahlung are
energy-dependent and become comparable at $E_{\rm kin} \agt $ 2 GeV. We also
calculate the polar angle anisotropy of the lepton spectrum.
