  Recent theoretical results on transport in a two-dimensional disordered
electron liquid with spin and isospin degrees of freedom are reviewed. A number
of experimental features in temperature dependence of resistivity at low
temperatures in Si-MOSFET, n-AlAs quantum well and double quantum well
heterostructures is explained. Novel behavior of low-temperature resistivity at
low temperature in electron systems with isospin degrees of freedom are
predicted.
