1.1 INTRODUCTION NEWLEAD is available for Silicon Graphics workstations. The software is supplied on magnetic medium with detailed installation instructions. Input and output files can be handled directly by the molecular modelling packages Macromodel, InsightII, and Sybyl. A graphic user interface is available for Accelrys's InsightII. You can find a general description of the program in our paper [1]. A few new features not covered in the paper are described below. H-bonds NEWLEAD recognizes H-bonds between all chemical structures (fragments, spacers, etc.). This reduces the danger of false negative results during the van der Waals check. receptor Optionally, you can include in your input any chemical structure as "receptor". The program builds spacers inside the receptor after checking for van der Waal violations. close contact connections To resolve van der Waals "violations" into bonds. movement of fragments The fragments are displaced to favour the connection of spacers.