A markerless motion capture technique is described for reconstructing three-dimensional biological motion. In the first stage of the process, an action is recorded with 2 CCD webcams. Then, the video is divided in frames. For each frame, the 2D coordinates of key locations (body joints) are extracted by the combination of manual identification (mouse pointing) and image processing (blobs matching). Finally, an algorithm computes the X-Y coordinates from each camera view to generate a file containing the 3D coordinates of every visible point in the display. This technique has many advantages over other methods. It does not require too specialized equipment. The computer programming uses open source software. The technology is based on an inexpensive portable device. Moreover, it can be used for different environments (indoor/outdoor) and living beings (human/animal). This system has already been tested in a wide range of applications, such as avatars modeling and psychophysical studies.