We present an overview of the most recent developments in polyphonic music retrieval and an experiment in which we compare two harmonic similarity measures. In contrast to earlier work, in this paper we specifically focus on the symbolic chord description as the primary musical representation and the similarity between sequences of these descriptions. In the experiment we compare a geometrical and an alignment approach to harmonic similarity, and measure the effects of chord description detail and a priori key information on retrieval performance. For this experiment a large new chord sequence corpus is assembled. The results show that a computational costly alignment approach significantly outperforms a much faster geometrical approach in most cases, that a priori key information boosts retrieval performance, and that using a triadic chord representation yields significantly better results than using more simple or more complex chord representations.