4-DIMENSIONAL STRING STRING DUALITY

We present supersymmetric soliton solutions of the four-dimensional heterotic string corresponding to monopoles, strings and domain walls. These solutions admit the D = 10 interpretation of a fivebrane wrapped around five, four or three of the six toroidally compactified dimensions and are arguably exact to all orders in alpha'. The solitonic string solution exhibits an SL(2, Z) strong/weak coupling duality which however corresponds to an SL(2, Z) target space duality of the fundamental string.