<p>Allometric relationships of body-part measurements permit structural comparison in terms of major-axis slopes and intercepts. They also enable least-squares prediction of one measure from another. Insectivorous mammals have long been divided into two phenetic groups: (a) dilambdodonts, including Erinaceidae, Soricidae, Talpidae, Macroscelididae and Tupaiidae, with a w-shaped ectoloph on upper molars; and (b) zalambdodonts, including Chrysochloridae, Potamogalidae, Tenrecidae and Solenodontidae, which have simpler v-shaped shearing crests on upper molars. Dilambdodonts have relatively large upper and lower molars (M¹ and M₁) for their body size, and first molar sizes that are highly correlated with body weight. The allometric coefficients for dilambdodont molar area and dilambdodont cranial length are slightly but significantly less than expected for a simple geometric relationship to a volume (body weight). High correlations mean molar size can be used to predict body weight in extinct dilambdodonts. Zalambdodonts have upper and lower molars that are generally smaller and more variable in relation to body size than those of dilambdodonts. Lower correlations mean zalambdodont molar size is less reliable for weight prediction. Cranial length is highly correlated with body weight in both groups, and hence a good predictor of weight.</p>