To investigate forms and functions of imprecise numerical expressions in biomedical slide talks, tokens were extracted from fifty-two talks presented at the 1979 annual meeting of the Federation of American Societies for Experimental Biology. Imprecise expressions include rounding, extreme rounding (to multiples of five or ten), ranges (both explicit and implicit), common fractions, and common multiples, all of which can be hedged, either simply or multiply. Imprecision can be occasioned by factors such as preliminary nature of results, small number of experimental animals, questionably applicable technique or apparatus, and inability to measure all members of a class. Rhetorically, imprecision foregrounds other, more precise quantities which the experimenter considers important, and thus, it can be seen as modality. Imprecision marks the talks as preinformation in Ziman's model of the social production of science and also as simultaneous popularization and peer communication. (Biomedical slide talks, imprecise numerical expressions, scientific rhetoric, modality, Zimanian social production of science)