Vacuum polarization about instantons

The one-loop contribution to the vacuum-to-vacuum transition amplitude in a multi-instanton configuration can be determined by the vacuum polarization current induced by the instantons. We compute these currents and the corresponding vacuum amplitudes for spin-O, -½, and - 1 fields in an arbitrary instanton configuration of winding numer $n$ which can be described by $5n$ parameters. The validity of the dilute-gas approximation is examined.