We have investigated the optimum conditions for the growth of NaxCoO2 single crystals by the optical floating-zone technique. A significant reduction in Na loss was achieved by using a high-pressure growth atmosphere. A high-pressure oxygen-rich atmosphere during crystal growth was found to reduce the presence of Co3O4 impurity phase in the grown crystal. The magnetic properties of powder and single crystal samples were measured by superconducting quantum interference device (SQUID) magnetometry and found to vary according to the preparation conditions. (C) 2004 Elsevier B.V. All rights reserved.