A quantitative model for Na partitioning between clinopyroxene and silicate melt, applicable in the range 0.1 MPa to 6.0 GPa, 1000-2000°C over a wide span of composition is presented. The model is tested against: 1) experimental data in the system diopside-albite from 0.1 MPa to 6.0 GPa; 2) analyses of clinopyroxene and glass from the mid-ocean ridge basalt-pyrolite sandwich experiments of Falloon and Green (1988); and 3) published experimental data from natural and synthetic systems. The model is in good agreement with the experimental data over the entire P-T range investigated. -from Authors