This article analyses molecular property calculation resources available on the Internet. The first section summarizes the on-line database resources that could be useful to search molecular and biological properties of chemicals, and indicates some principal databases with physicochemical, thermochemical, toxicity, cancer and HIV data. The second section overviews popular standalone programs for calculation of molecular descriptors. Some of these programs can be downloaded for free and used as standalone applications for calculation of molecular descriptors. The third section describes on-line tools for the prediction of molecular properties, activities and calculation of molecular descriptors. Analysis of emerging tools that can be useful to developing new on-line servers for the prediction of molecular parameters and properties is also given.