Diagnostic leaching is an analytical tool which has been developed at the Anglo American Research Laboratories (AARL) during the mid 1980＇s. This technique has been used widely by various institutions during the last eight years with mixed results, mainly due to insufficient information regarding the technique or to ignorance with regard to the development of a test procedure and the analysis of results. The technique had been refined to some degree during the last few years at the Department of Chemical Engineering of the University of Stellenbosch. This paper contains all the relevant information required for implementing the technique at a laboratory successfully, and some background information to interpret results obtained from this procedure is also included. Evidently, the mineralogy of the matrix material (sample) is the main factor that determines which steps in such a technique are necessary in order to obtain optimal results. Diagnostic leaching is only a tool to help the mineralogist or metallurgist to get a much clearer view of the deportment of gold in an ore or a sample. This will enable him or her to design new flowsheets, alter existing ones and identify problem areas in plants and unit operations.