One hundred and forty-three new chemical analyses of Hawaiian lavas are presented. These demonstrate that the ‘primitive’ rocks of all Hawaiian volcanoes are tholeiitic, that there is no difference between those of volcanoes that later gave rise to hawaiites and ankaramites and those that later produced mugearites and trachytes, that there is complete chemical gradation between tholeiitic and alkalic basalts, and that tholeiitic and alkalic basalts are interstratified in a thin transition zone. Transition from tholeiitic to alkalic basalt occurs in the upper part of the caldera-filling sequence in the volcanoes that produced hawaiite, and in the upper part of the shield below the unconformity at the base of the mugearitic cap in the volcanoes that produced mugearite and trachyte. Within the tholeiitic and alkalic suites, respectively, differentiation is largely controlled by fractional crystallization. The felsic end member of the alkalic suite is soda trachyte; that of the tholeiitic suite is rhyodacite.