Abstract. Let H be the Iwahori-Hecke algebra associated with Sn, the symmetric group on n symbols. This algebra has two important bases: the Kazhdan-Lusztig basis and the Murphy basis. While the former admits a deep geometric interpretation, the latter leads to a purely combinatorial construction of the representations of H, including the Dipper-James theory of Specht modules. In this paper, we establish a precise connection between the two bases, allowing us to give, for the first time, purely algebraic proofs for a number of fundamental properties of the Kazhdan-Lusztig basis and Lusztig's results on the a-function.