A positive effect of ultrasound on crystallization has been shown for many applications especially on small scale. Predictable scale-up of sonocrystallization is a challenge due to the inherent dependency of ultrasound on scale. The presented research discusses the experimental application of ultrasound to induce nucleation at low supersaturation for start-up of evaporative batch-wise crystallization of ammonium sulfate in a 75-L draft tube (DT) crystallizer. A comparison is made with a conventional start-up procedure using primary nucleation or seeding. Ultrasound is applied in two geometrically different vessels of 1.2-L connected to a 75-L DT crystallizer. Application of ultrasound for start-up of a 75-L DT crystallizer shows that an optimum amount of ground seeds is better capable to suppress nucleation. A challenge for future research is to improve the efficiency of ultrasound to produce a large number of nuclei for start-up of batch crystallization at larger scale. (C) 2011 American Institute of Chemical Engineers AIChE J, 57: 3367-3377, 2011