The corrections for Lorentz and polarization factors for trial and error crystal structure computations are discussed, following the general method recently presented for correcting x‐ray diffraction data used in Fourier syntheses. The Lorentz correction has the form (1/S) csc y&hook;, whereSis a scale constant characteristic of the reciprocal lattice level and whose form varies with the method of recording the data. The scale constant is eliminated by appropriate timing of the exposure. When many trial and error computations have to be made, there are advantages in using a scheme involving a correction factor (csc y&hook;)½instead of csc y&hook;. Tables are provided for these functions, for the polarization correction and for the combined Lorentz‐polarization correction which is used in the special case of zero‐level photographs. Tables are also provided for the functions (h2+k2)½and (h2+k2+hk)½, which are useful for computing the argument for the zero‐level corrections of tetragonal and hexagonal crystals.