The new program ANODE estimates anomalous or heavy-atom density by reversing the usual procedure for experimental phase determination by methods such as single- and multiple-wavelength anomalous diffraction and single isomorphous replacement anomalous scattering. Instead of adding a phase shift to the heavy-atom phases to obtain a starting value for the native protein phase, this phase shift is subtracted from the native phase to obtain the heavy-atom substructure phase. The required native phase is calculated from the information in a Protein Data Bank file of the structure. The resulting density enables even very weak anomalous scatterers such as sulfur to be located. Potential applications include the identification of unknown atoms and the validation of molecular replacement solutions.