An analytical study is described of the magnetic-field system in a d.c. linear motor. The equations derived are solved by numerical techniques based on a finite-difference approximation. A modification of existing methods is adopted to deal with heterogeneous regions of permeability. The computed flux profiles are shown to compare favourably with experimental results obtained on a 2-pole machine, including the effects of armature reaction. The results are used in tahe derivation of the developed force and dynamic characteristics of a loaded machine, and the theoretical results are again shown to agree closely with experimental results.