A new mixing method, which can mix some hundred microliters of liquid in a vessel without any physical contact, was developed. This mixing method used free surface waves in a vessel generated by ultrasound irradiation from outside the vessel. First, feasibility of circulation flow induced by waves was discussed with a numerical simulation. The mixing mechanism was then experimentally verified by flow visualization using a dye. Next, the method was applied to mixing serums and reagents. The serum-reagent mixture was visualized by using the Schlieren method, and the mixing performance was quantified from the visualized images. The experimental results show that the new mixing method is suitable for volumes of serum-reagent mixtures ranging up to 180 mu l. Finally, by implementing the new mixing method in a standard chemical auto-analyzer, a new kind of chemical auto-analyzer that does not suffer cross-contamination between samples was produced. (c) 2005 Elsevier Ltd. All rights reserved.