A new laser-based technique for measuring instantaneous three-dimensional species concentration distributions in turbulent flows is presented. The laser beam from a single laser is formed into two crossed light sheets that illuminate the area of interest. The signal light from both planes is detected with a single camera via a mirror arrangement. Image processing enables the reconstruction of the three-dimensional data set in close proximity to the cutting line of the two light sheets. Volume visualization by digital image processing gives unique insight into the three-dimensional structures within the turbulent processes. Three-dimensional intensity gradients are computed and compared to the two-dimensional projections obtained from the two directly observed planes. We apply this technique to measurements of the hydroxyl (OH) concentration distribution by laser-induced fluorescence (LIF) in a turbulent methane-air flame upon excitation at 248 nm with a tunable KrF excimer laser. Further measurements address the three-dimensional distribution of toluene-LIF in a turbulent, non-reactive mixing process of toluene and air.