  We derive the general form for a three-dimensional scale-invariant field
theory with N=6 supersymmetry, SU(4) R-symmetry and a U(1) global symmetry. The
results can be written in terms of a 3-algebra in which the triple product is
not antisymmetric. For a specific choice of 3-algebra we obtain the N=6
theories that have been recently proposed as models for M2-branes in an R^8/Z_k
orbifold background.
