Tracer testing is generally regarded as the most reliable and e.cient method of gathering surface and subsurface hydraulic information. This is especially true for karstic and fractured-rock aquifers. Qualitative tracing tests have been conventionally employed in most karst sites in the United States. Quantitative tracing tests are employed sparingly at karstic sites in the United States, although it is widely recognized that they provide a wealth of hydraulic and geometric data and are commonly employed in nonkarstic hydrological systems. Quantitative tracer tests are regarded as more difficult and time-consuming than qualitative tracing tests, which is a fallacy that needs to be overcome. The benefits of quantitative tracing far outweigh any additional expenses incurred for all hydrologic systems. An efficient, reliable, and easy-to-use computer program, QTRACER2, designed to run on PCs running any version of Microsoft Windows.