This paper presents some novel interface techniques for the visualization of scalar field data in virtual reality (VR) environments. In particular, we discuss the direct manipulation of isosurfaces and cutting planes and give general guidelines for design of user interfaces and algorithms for scientific visualization in virtual environments. This work was motivated by the need to visualize scalar field data from computational fluid dynamics (CFD) calculations interactively in the Virtual Wind Tunnel at NASA Ames, but the techniques are applicable to other problem areas, including medical imaging and geological and mathematical visualization. KEYWORDS: scientific visualization, virtual reality, direct-manipulation interfaces, scalar fields, isosurfaces, cutting planes INTRODUCTION Data sets in scientific visualization often take the form of 2D and 3D scalar fields. For example, height data on a 2D topographic map, temperatures in the fluid flow over a wing, and the density information ..