The PREscore computer program has been developed to assist Superfund site assessment investigations in Hazard Ranking System (HRS) site scoring. The HRS is used to assess the relative threat associated with actual or potential releases of hazardous substances to ground water, surface water, soil, and air. The HRS is the primary means by which EPA evaluates sites for the National Priorities List (NPL), the list of the hazardous waste sites that are eligible for remedial funding under the Superfund program. PREscore is designed to be user-friendly, operating via hierarchically-dependent spreadsheets that allow data to be entered quickly and efficiently. Significant program features include: Instant score calculation and continuous score display; Multiple site-scenario testing capability; Extensive Help screens; Comprehensive documentation ability; PREscore fully automates the HRS, allowing for the entry and evaluation of all types of site-related information including sampling data, waste quantities and waste characteristics, physical parameters of the site, population data, and administrative information. In addition, PREscore contains HRS-related hazardous substance information derived from the Agency's Superfund Chemical Data Matrix (SCDM), which includes substance characteristics such as toxicity and persistence, and concentration benchmarks for the substances commonly encountered at Superfund sites (Currently over 300 substances). PREscore is accompanied by PREprint, a program that produces an extensive documentation record for sites evaluated by PREscore. PREscore requires no specialized computer experience and has no additional software requirements. However, PREscore does require the user to be familiar with the HRS. PREscore Version 3.0 updates the previous PREscore versions 2.0 and 1.1 with program modifications and information on hazardous contaminants from the June 1994 Superfund Chemical Data Matrix.