Pathologists typically analyze biopsy specimens and report their opinions in a qualitative fashion. Clinical information, often fragmentary in character, is implicitly linked with the histologic findings, and interpretations are couched in ambiguous language: "consistent with," "highly suggestive of," "may represent," or "cannot exclude." Only pathognomonic or normal findings are reported in an unequivocal fashion. In this paper we compare the analysis of biopsy material by a conventional method and by a numerical, probabilistic technique. We suggest that applying a probabilistic technique can considerably improve the precision of tissue diagnosis and can greatly facilitate the communication of pathologists with clinicians and with each other. Probabilistic analysis is also likely to be of substantial value in improving the interpretation and reporting of x-ray and nuclear-medicine studies.