A portable transcranial magnetic stimulation (TMS) prototype was designed and constructed for use in clinical trials to manage the pain associated with migraine with aura. In this system, a half-sinusoid (optionally a full-sine) TMS pulse is delivered into a circular coil. The pulse triggering is controlled by a switch in the coil handle. The pulse intensity and polarity are adjustable. Measured pulse parameters (period , maximum magnetic field at coil center ) corresponded to expected values and were in the range described for commercially available TMS apparatus. The maximum current density, computed 3 cm below the coil using a simple model of brain anatomy, was approximately 1.9 times the motor threshold, thus ensuring a sufficient margin for reaching the neuronal threshold in the target area.