An algorithmic process for the detection and marking of clustered calcifications in digitized film-screen mammograms has been applied to mammograms from 50 clinical cases sampled at two digitization levels, in both the craniocaudal and mediolateral views. In all but one case the detector accurately located suggestive clusters found by radiologists in normal screening. In five cases additional clusters were also found by the detector. The detector has a negligible false-positive rate for the detection of clustered calcifications, although it is sensitive to clusters of emulsion defects displayed as artifactual calcification densities in the original film. The detector is flexible in structure and is easily adapted to various calcification/cluster criteria. The detector shows considerable promise when applied to clinical examples but will require refinement before formal testing.