The weak production of Λ ’s in nucleon-nucleon scattering is studied in a meson-exchange framework. The weak transition operator for the N → N N Λ reaction is identical to a previously developed weak strangeness-changing transition potential Λ → N NN that describes the nonmesonic decay of hypernuclei. The initial NN and final YN state interaction has been included by using realistic baryon-baryon forces that describe the available elastic scattering data. The total and differential cross sections as well as the parity-violating asymmetry are studied for the reaction p → n p Λ . These observables are found to be sensitive to the opening of the Σ production channel, the choice of the strong interaction potential, and the structure of the weak transition potential.