  A new type of sl_3 basic hypergeometric series based on Macdonald polynomials
is introduced. Besides a pair of Macdonald polynomials attached to two
different sets of variables, a key-ingredient in the sl_3 basic hypergeometric
series is a bisymmetric function related to Macdonald's commuting family of
q-difference operators, to the sl_3 Selberg integrals of Tarasov and Varchenko,
and to alternating sign matrices. Our main result for sl_3 series is a
multivariable generalization of the celebrated q-binomial theorem. In the limit
this q-binomial sum yields a new sl_3 Selberg integral for Jack polynomials.
