Boron and lithium abundance distributions are very different in the sedimentary and volcanic sections of the VC-1 core hole, Valles caldera, New Mexico. In the sedimentary section the wide variations in boron and lithium abundances probably reflect both diagenesis and introduction of these elements in early hydrothermal fluids. Late, higher-temperature fluids appear to have leached boron and lithium from some rocks adjacent to fault zones and aquifers. The correlation of boron with lithium suggests that these elements behave in similar ways during diagenesis and hydrothermal alteration. The small variation of boron and lithium abundances in most of the vitreous volcanic rocks from the upper part of the core implies that their source was relatively homogeneous. Following primary devitrification, boron appears to have been stable, but lithium was mobile. Boron may have been stabilized by the development of boron-bearing submicroscopic phenocrysts in the lavas, or boron may be less soluble than lithium in relatively cool groundwater. ¿ American Geophysical Union 1988