The chemical composition of suites of basaltic lavas combined with field observations and petrography can give information on the following topics: l) mineralogy and approximate composition of the mantle from which the basalts were melted, 2) nature of the subvolcanic plumbing; evidence for the depth at which magma is stored before eruption, and 3) information on the kind and amount of fractionation that takes place before eruption. Three different suites of intraplate tholeiitic lavas have been studied in order to compare and contrast the inferences regarding subjects 1-3 above. These are 1) lavas from Kilauea, an oceanic island volcano; 2) Leg 37 basalts, erupted from the Mid-Atlantic Ridge spreading center; and 3) Grande Ronde basalt (Columbia River Basalt Group), representing a continental suite.