The sensitivity and precision of teflon-imbedded CaS04:Dy microthermoluminescent dosimeters (micro-TLDs) were determined. The micro-TLDs were sectioned from miniature TLDs (200 jumX400 //mX 5 mm) that were fabricated using standard techniques. In order to measure absorbed dose, the miniature TLDs can be implanted directly into tissues (e.g., tumor xenografts) that have received injections of radiolabeled monoclonal antibodies. Micro-TLDs recovered from tissue sections cut with a microtome can be read out to determine local absorbed dose. The precision of dose estimation was quantified for uniformly irradiated 32-, 96-, and 192-/zm TLD chips; coefficients of variation ranged from 22% to 41%, depending on chip size. The coefficients of variation were reduced to less than 12% using individual relative sensitivity factors for each micro-TLD. The spatial resolution of the micro-TLDs was studied by placing miniature TLDs across the sharp penumbral region of a linear accelerator x-ray field. TLDs were sectioned into 32-/zm chips which were read out to determine the relative absorbed dose. The sharpness of the penumbra was readily quantified by the micro-TLDs. © 1991, American Association of Physicists in Medicine. All rights reserved.