hard to answer without additional information on what kind of "relationship" you are interested in ; however, you could try a simple Engle-Granger test for co-integration of the two series ... as a starter !
Engle-Granger test is also known as Engle-Granger two step error correction model (ECM) !
So, yes, you could try that as it is the "vanilla" approach to the extraction of a "relationship" between time series ; of course, cointegration is a very tight kind of "relationship" and the test may fail for a zillion of reasons (you can't expect two time series to behave as gently as the drunken lady and her dog !)
more details here if you are interested (but maybe you know this already and my suggestion is too simplistic!) :