  The cross sections for the reactions pp -> p Lambda^0K^+ and pn
  -> n Lambda^0K^+ are calculated near threshold of the final states. The
theoretical ratio of the cross sections R = sigma(pn -> n Lambda^0K^+)/
sigma(pp ->p\Lambda^0K^+) = 3 shows the enhancement of the pn interaction with
respect to the pp interaction near threshold of the strangeness production N
Lambda^0K^+. Such an enhancement is caused by the contribution of the np
interaction in the isospin-singlet state, which is stronger than the $pn$
interaction in the isospin-triplet state. For the confirmation of this result
we calculate the cross sections for the reactions pp -> pp pi^0, pi^0 p ->
Lambda^0 K^+ and pi^-p -> Lambda^0 K^0 near threshold of the final states. The
theoretical cross sections agree well with the experimental data.
