Ultrasound provides us with a step function for nucleation that is not sensitive to the initial supersaturation. A strong reduction in induction times from batches of ammonium sulphate solutions at different insonation intervals t(N) resulted. A narrow mono-dispersed distribution with L-50 = 6.0 mu m was measured for a batch at t(N) = 0.5 min. A first attempt was made to correlate the collapse pressure of the cavitating bubbles with the nucleation rate. The calculated induction times for ammonium sulphate were compared with the values measured in a specially designed cavitator, where a standing wave was created. The values did not match, which might be caused by the large number of uncertainties in the assumptions made in the calculations and the limitations of the detection method. Experiments are therefore always needed to calculate the exact number of nuclei that are formed. The calculations however, can help in deciding whether ultrasound may serve as an adequate method to sufficiently increase the nucleation rate. (c) 2006 Elsevier B.V. All rights reserved.