Filamentous actin (F-actin), one of the constituents of the cytoskeleton, is believed to be one of the most important participants in the mechanical integrity and motion of eukaryotic cells. The viscoelastic moduli of F-actin networks have traditionally been measured, in bulk, by imposing a small oscillatory mechanical strain and quantifying the resulting stress. Microrheology is a method developed in the last decade for measuring the viscoelastic moduli of gels. In this method, the elastic properties of complex fluids are inferred from the motion of small colloidal particles incorporated into the gel. Over the years, many techniques have been developed for tracking those particles and measuring the rheological properties of in-vitro polymer solutions. We report a new technique for high frequency and high resolution tracking of colloids in three dimensions. With the method of digital holographic imaging, we use a high speed camera for recording the holograms. The digital reconstruction of the particles’ images enables us to track embedded beads in 3D with tens of nanometer resolution, in high frequency. This tracking technique provides accurate passive measurements of the rheological properties of F-actin networks in high bandwidth over 5 decades.