The behaviour of a perturbed capillary jet is experimentally determined by studying the jet from the time it emerges from a small hole to the point at which individual droplets of fluid begin to form. Under any particular set of externally applied experimental parameters, i.e. jet velocity, disturbance wavenumber and amplitude, there is a unique, minimum time to this breakup into drops. This characteristic is needed to relate the magnitude of the input voltage to the modulating device and the output velocity perturbation that it produces. Using this relationship we then compare the experimentally produced profiles of jet shape to corresponding ones calculated by using the theory of Chaudhary & Redekopp (1980). The agreement is satisfactory, especially for small values of input voltage. Then, in the neighbourhood of the cutoff wavenumber, we show that the predicted linear growth of the jet profile is also reproduced in the experimental model.