First-principles total-energy band theory is used to study the onset and the large-volume limit of magnetic behavior for the 3d transition metals constrained to the bcc crystal structure. It is found that all 3d transition metals from Sc to Ni undergo second-order, first-order, or composite second- and first-order transitions from nonmagnetic to magnetic behavior with increasing volume. An approximate Stoner analysis is used to interpret the structure of the transitions. As a function of volume, calculated magnetic moments generally increase and tend toward the free-atom limit in the local-spin-density approximation, and are consistent with Hunds rule. Calculated d-band widths vary as r-5 over a wide range of volumes, in agreement with Heines theoretical results. © 1988 The American Physical Society.