The need to perform spatial manipulations (like selection, translation, rotation, and scaling) of virtual 3D objects is common to many types of software applications, including computer-aided design (CAD), computer-aided modeling (CAM) and scientific and engineering visualization applications. In this work, a prototype application for manipulation of 3D virtual objects using free-hand 3D movements of bare (that is, unmarked, uninstrumented) hands, as well as using one-handed and two-handed manipulation gestures, is demonstrated. The user moves his hands in the work volume situated immediately above the desktop, and the system effectively integrates both hands (their centroids) into the virtual environment corresponding to this work volume. The hands are being detected and their posture recognized using the Viola-Jones detection method, and the hand posture recognition thus obtained is then used for switching between manipulation modes. Full 3D tracking of up to two hands is obtained by a combination of 2D flocksof-KLT-features tracking and 3D reconstruction based on stereo riangulation.