Interest has grown during the past several years in the functional analysis of chipped stone tools by microscopic inspection of damage traces which result from intentional use and other agencies (KEELEY 1976; ODELL 1975; TRINGHAM et al 1974). The researches of KEELEY and of TRINGHAM and associates have been instrumental in establishing the prerequisite experimental criteria for interpreting the 'functions' of prehistoric stone implements. The observation of microwear polishes on flint tools has been shown to be particularly promising (KEELEY and NEWCOMER 1977). This presentation summarizes the principal results of an on-going experimental project designed to widen the application of interpretive microwear polishes from one type of flint (British chalk flint, used by KEELEY) to several types of flint, as well as to obsidian. The materials in question were obtained from the Argolid region of southern Greece (the flints) and from the Aegean island of Melos (the obsidian). The results of the experimental studies will be applied to the microwear analysis of flint and obsidian tools from a major prehistoric site in the southern Argolid, Franchthi Cave (JACOBSEN 1976, 1973). The three grades of flint collected from the general region of the cave, distinguished by grain size (fine, medium-fine, and medium-coarse), provide a realistic sample of the great diversity of flint types present in the prehistoric collection. This diversity, however, is greatly reduced when considering only the factor of grain size. The categories are easily established by visual inspection of fresh breaks (from 'shiny and smooth' to 'dull and coarse') and by viewing such surfaces at high magnification (ca 300x, Wild M50 metallurgical scope) and noting the prevalence of natural bright spots as opposed to darker background areas. Indeed, it is imperative to know what microscopic bright spots occur naturally on a given type of flint, to avoid confusing them with microwear polishes. The results of over 120 experimental tests conducted thus far (3/79) with flakes of the three flint types on a wide variety of materials (stone, bone, antler, wood, hide, vegetal matter, meat) indicate a striking regularity in the developmental processes and resultant patterns of microwear polishes across all flint types. As noted by KEELEY, under high magnification one can distinguish, on tools of the same flint, the various distinctive polishes produced by such materials (provided the tool is used for at least