Precipitation is a promising method for the economic production of commercial amounts of nanoparticles because it is fast, and operable at ambient temperature. However, process control - due to the rapidity of the involved processes of mixing, nucleation, growth, and agglomeration - and stabilization against agglomeration represent challenges. This paper shows how these, challenges can be successfully handled. The focus of this work is therefore set on how to tailor the particle-size distribution in continuous precipitation. Precipitation experiments with barium sulfate in a T-mixer are presented. It was found that the size of the precipitated primary particles is strongly dependent on the mixing intensity. On increasing the mixing intensity, it was possible to generate particles of approximately 50 nanometers in diameter. The second challenge, to stabilize the particles against agglomeration, was successfully met by adsorbing potential-determining ions on the particle surfaces, i.e., by increasing repulsive particle interactions. Thus, stable suspensions of barium sulfate nanoparticles were obtained.