This work proposes a preprocessing technique to enhance microcalcifications on digitized mammographic images based on a frequency domain band pass Butterworth filter. The parameters for the filter are obtained from specifications of cutoff frequency and band width that define the dimension of the structures that should be enhanced by the filter. In this case, it was adjusted to enhance the corresponding band of typical sizes of microcalcifications in mammographic images, in order to improve the efficiency of a computer-aided diagnosis (CAD) scheme. Results with a well known processing technique to detect microcalcifications showed better performance using images enhanced by the proposed filter.