Results from refraction experiments have been combined with local earthquake data to produce a preliminary model for the structure of the New Hebrides arc-trench system. Maximum crustal thickness of about 28 km occurs beneath the island ridge. The crust is unusually thick (about 10 km) in the zone seaward (westward) of the trench, where the velocity of the deepest layer is 7.0 km/s. The crustal thickness of the Fiji plateau, east of the New Hebrides ridge, varies between 5 and 7 km. The velocities of th materials that form the inner trench wall are similar to those found in the island ridge. A Zone of relatively high velocity (4.1 km/s) is encountered at a depth of about 1 km beneath the arc-trench slope. This zone thicknes toward the trench and is overlain by material with velocity typical of surficial sediments (?2 km/s). This may be an accretionary deposit, or it may be of volcanic origin.