Interactions on the nanometer length scale are very important in determining the performance of microfluidic devices and micron-sized machines. Thus, the omnipresent van der Waals force will play a pervasive role. It is less well recognized that, within a fluid, the presence of adsorption can lead to additional adsorption-induced forces of similar strength. We discuss these issues in this publication. (C) 2003 Elsevier B.V. All rights reserved.