Poly(2-vinylpyridine) microgel particles and polystyrene latex are aggregated in an alternating electric field to produce a new class of microrods. An electric field simultaneously accelerates the aggregation of oppositely charged particles, and templates the aggregates into linear structures. Rods up to 100 mu m in length can be reversibly extended by 20% by a change in solution pH because of the swelling properties of the microgel particles (see figure).