The nucleation and growth of 0.91PZN-0.09PT single crystals was investigated by the slow-cooling flux technique using PbO flux and by means of hot-stage microscopy. The results showed that during the initial stages of cooling small crystals of cubic morphology nucleated first. On further cooling, preferential growth developed along the four (1 1 1) corners of the cubic crystals, and one of the corners eventually outgrew the rest into a large arrowhead-shaped crystal against the heat flow direction. The terrace nature of the arrowhead crystals suggests that kinetic roughening, possibly promoted by a critical supersaturation in the solution, is the mechanism of the fast growth of PZN-PT crystals. The present work shows that under favorable conditions, such as with a high inverse temperature gradient and a solution cooling rate of about 1 degrees C/h, large-sized PZN-PT crystals measuring 3.0 x 2.5 x 2.0 cm(3) can be reproducibly grown from PbO flux by the slow-cooling technique.