We calculate the contribution to the muon anomaly induced by new Yukawa couplings involving heavy-matter E6 fields predicted in the framework of superstring theories. We analyze a few models found in the current literature and show that for some of them the effect is on the order of the standard weak contribution. We produce a specific example where the effect could be even larger. Thus, we conclude that an improved (g−2)μ experiment should be sensitive to such effects, if they happen to exist.