  We discuss experimental implications of extending the gauge structure of the
Standard Model to include an additional U(1) interaction broken at or near the
weak scale. We work with the most general, renormalizable Lagrangian for the
SU(2)\times U(1)\times U(1) sector, with emphasis on the phenomenon of gauge
kinetic mixing between the two U(1) gauge fields, and do not restrict ourselves
to any of the "canonical" Z' models often discussed in the literature.
Low-energy processes and Z-pole precision measurements are specifically
addressed.
