Tracer tests are generally regarded as being the most reliable and efficient means of gathering subsurface hydraulic information. This is true for all typed of aguifers, but especially so for karst 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 karst sites in the Unites States, although it is widely recognized that they provide a wealth of hydraulic and geometric data on subsurface conditions. Quantitative tracer tests are regarded as more difficult and time-consuming than qualitative tracing tests, which is a fallacy to be overcome. The benefits of quantitative tracing far outweigh any additional expenses that are incurred. An efficient, reliable and easy-to-use computer program, QTRACER, designed to run on PCs running any version MS-DOS or Windows, has been developed to facilitate tracer-breakthrough curve analysis. It solves the necessary equations from user-generated data input files using robust integration routines and by relying on established hydraulic models. Additional features include dynamical memory allocation, ability to extrapolate late-time data using any one of three difficult methods, two separate methods for handling oversized time-concentration data files, and a powerful interactive graphics routine. Two other programs are included to facilitate the use of QTRACER. The first, NDATA, allows the user to interpolate either their time-concentration or time-discharge data files to fill in data gaps. The second programs, AUTOTIME, allows the user to convert time-concentration data files recorded using military time into sequential decimal time as required by QTRACER. Files created by these two programs may be appended to the bottom of a sampling station data file that can be read by QTRACER.