A four-wire probe and a novel signal interpretation procedure were developed for the simultaneous measurement of three instantaneous velocity components in a three-dimensional, turbulent, flow field. The new probe consists of four sensors slanted at 50 degrees with respect to the centreline axis and arranged in a double V configuration; each V configuration is perpendicular to the other. The implementation of this technique and the inclusion of the fourth wire remove ambiguity and resolve most of the problems affecting the performance of the three-wire probe and, in particular, prevent the occurrence of conditions of non-uniqueness. The new technique was tested in turbulent pipe flow and in a swirling jet issuing into a co-flowing stream. Some of the results obtained in the swirling flow are compared with previous measurements, which were obtained using a five-tube pressure probe. The agreement between both sets of data is shown to be very good.