Magnetic modeling of the Sudbury Structure (SS) has been undertaken using the geometrical and lithological framework provided by high-resolution seismic reflection data. This initial constraint was required because of the complex magnetic properties exhibited by rock units of the SS. Locally remanent magnetization (NRM) dominates over induced magnetization, and the orientation and amplitude of the NRM vector varies both between and within individual rock units. The use of measured magnetic susceptibility and NRM values afforded an important constraint in the modeling process, and provided a valuable insight into the genesis of the various magnetic anomalies. The magnetic anomaly profile along the Lithoprobe Transect across the SS appears to arise from three main sources: a) a broad regional magnetic anomaly ascribed to a more magnetic layer of the Levack Gneiss Complex subjacent to the base of the Sudbury Igneous Complex (SIC); b) a prominent magnetic high associated with the southern contact between the Onwatin and Onaping Formations, believed to reflect a zone of hydrothermal mineralization; and c) a magnetic high associated with the southern contact between the SIC and the Huronian mafics is related to the juxtaposition of rock units produced by northward directed thrusting and an enhanced NRM signature in the basal unit of the South Range Norite. ¿ American Geophysical Union 1994