This paper presents a theoretical study of conjugate heat/mass transfer from a circular cylinder with an internal heat/mass source and a surrounding fluid flow. The heat/mass source consists of a constant temperature/concentration wire imbedded in the cylinder center. A finite difference method discretizes the equations. The multigrid method solves the discrete system. Numerical investigations were carried out for cylinder Re numbers equal to 2 and 20. The values of the Pr number were selected such that the product Re x Pr is constant and equal to 100. The main aspect analysed is the influence of the conductivity ratio on the local and average Nu numbers at different values of the wire diameter. (C) 2004 Elsevier Ltd. All rights reserved.