The paper studies fluid and mass transfer flow of blood in a single blood vessel. Blood is modeled as a Newtonian fluid of constant properties while the blood vessel is modeled as a long tube of circular section of slowly varying radius. The coupled governing equations are solved using a series expansion about a small parameter ε, (ε≪1) characterizing the radius variation, and expressions are obtained for the velocity, temperature, concentration, shear stress and species transfer at the wall of the blood vessel. Results obtained show that the concentration of species in blood vessels drifts from the axis towards the walls of the blood vessel in qualitative agreement with existing clinical observations.