Every stringed instrument player knows that new nylon strings rapidly go out of tune, whereas metal strings do not. This is because metal strings show elastic behavior while nylon is viscoelastic. We present an experiment suitable for the undergraduate laboratory in which we measure the stress relaxation in a nylon string by monitoring the frequency of the note produced and show that it can be adequately described in terms of a model using Maxwell elements in series. © 1997 American Association of Physics Teachers.