A brief overview on recent model calculations for near threshold pion
production in nucleon-nucleon collisions is given. Results from our ow
n investigations of the reactions pp --> pp pi(0) and pn --> d pi(0) a
re presented. Direct production, heavy meson exchange and pion rescatt
ering are taken into account. For the latter a T-matrix obtained from
a microscopic model of the pi N interaction is employed. We obtain a s
ignificant contribution from rescattering, but not enough to describe
the data for pp --> pp pi(0). The missing production rate can be provi
ded by heavy meson exchanges. For the first time the effect of off-she
ll rescattering is investigated for the reaction pn --> d pi(0). Isosc
alar rescattering in combination with isovector rescattering is able t
o describe the s-wave Production data. We confirm that heavy meson exc
hanges are negligible in this reaction.