In this work the effect of initial twist on wave characteristics in a prestressed elastic thin tube filled with a viscous fluid is studied. Initially the tube is subjected to a large static transmural pressure P-i, an axial stretch lambda(z), and a twisting moment M. Assuming that in the course of fluid flow a small incremental axially symmetric disturbance is added on this field the equations governing the incremental motion are obtained both for elastic tube and viscous fluid. Seeking a harmonic wave type of solution to the field equations and using the boundary conditions the dispersion relation is obtained for long-wave approximation. Considering the difficulties of analytical treatment of the dispersion equation a numerical analysis is presented and the results are discussed. (C) 1997 by Elsevier Science Inc.