Effects of experimental diets on microscopic dental wear in the American oppossum show that it might prove difficult to distinguish the microwear produced by an insectivorous diet from that produced by some kinds of herbivorous ones. Wear caused by gritty diets and those containing plant opal, although they might be confused with one another, are easily distinguished from other sorts of dietary wear. These conclusions have been challenged on the basis that possibly sufficient time was not allowed in the experiments for diagnostic wear patterns to emerge. Additional data reported here show that this is not so. Even in control animals, fed a relatively soft unabrasive diet, enough time elapsed to produce significant dental wear. A new technique is described which for the first time allows the study of changing patterns of microscopic wear in a living animal over a period of time, thus allowing each animal to serve as its own control. A solution containing a broad-spectrum proteolytic enzyme when applied to the teeth of an anesthetized animal removes the proteinaceous coat (pellicle) which will otherwise obscure wear scratches. Precision dental impressions can then be made which reveal the details of the pattern of microwear on the teeth.