Low dose cryoelectron microscopy has been used to record images and electron diffraction patterns of frozen hydrated crystals of the single-stranded DNA binding protein gp32*I. Fourier transforms from 13 image areas, corresponding to approximately 40,000 unit cells, were aligned by a minimal phase residual search and merged by vector addition in reciprocal space. Phases from the resulting composite transform were combined with amplitudes from electron diffraction patterns to reconstruct the projected mass density of the gp32*I crystal at 8.4 A resolution.