Zinc oxide crystals grown in a single basic mineralizer in hydrothermal autoclaves are of poor quality. The crystals are transparent. pale green or pale yellow in color depending on different technical growth conditions. The quality of crystals under different conditions was observed by X-ray rocking curves measurement. The use of ultra-pure nutrient improves their perfection and purity. Zinc oxide bulks that were grown by the hydrothermal method in a mixture of KOH and LiOH aqueous solutions are of good quality. (C) 2005 Elsevier Ltd. All rights reserved.