Volcanic rocks collected on flowline traverses on the flanks of the East Pacific Rise (EPR) document changes in axial magma chemistry with time, providing a record of the thermal history of axial magma chambers (AMC). We present data for a sample set of closely spaced (1--2 km) samples along EPR flowlines at three localities out to ~800 ka showing both steady (constant average temperature) and non-steady state behavior of magma chambers on time scales of 200--500 ka. Though based on only three symmetrical traverses so far, it appears that magmatically robust ridge locations (11¿20'N and 9¿30'N) have steady state chambers, whereas a magmatically starved axis (10¿30'N) shows large temperature changes with time. These observations provide a new petrologic perspective to the ongoing debate regarding the significance and causes of morphologic variations along the axis of the East Pacific Rise. ¿ American Geophysical Union 1996