Leg 83 of the Deep Sea Drilling Project represents the deepest penetration of undisturbed marine crust yet achieved, providing samples from the lower part of the extrusive layer and the upper 300 m of the sheeted-dike complex. We present here measurements of the magnetic properties of rocks from Leg 83 and address the question of their suitability as sources for marine magnetic anomalies. We find that, due to extensive hydrothermal alteration, the extrusive part of the Leg 83 section is insufficiently magnetized to be part of the magnetic source layer. The sheeted-dike complex, on the other hand, does have sufficient magnetization and, contrary to recent models of marine magnetization based on ophiolite studies, may be a contributor to magnetic anomalies. The strong dependence of magnetic properties on the alteration history of the rocks, however, makes extension of these results to other regions problematical.