LDV measurements were carried out for flows of a Newtonian fluid (water) and a shear-thinning elastic fluid (a PAA-solution) in a converging channel which was designed to have a constant rate of extension for extensional viscometry. Measurements were made at several stations along the channel and at Various flow-rates, yielding Reynolds numbers ranging from 20 to 1500. For both fluids and for Re higher than 10(2), the data showed that centerline velocity increased linearly in the flow direction, confirming that the channel creates constant rates of extension in the core flow. Predictions of velocity profiles from a quasi-similarity solution agreed well with the water profiles. The same theory, modified for power-law fluids, was much less successful in predicting the profiles for the PAA solution. One cause of the discrepancy was shown to be early development of the velocity held, generated by fluid elasticity.