The electrochemical technique with the ferri-ferrocyanide system has been used to study mass transfer at high Schmidt numbers in a straight pipe and a Y-bifurcation flow model, with the latter being relevant to arterial blood flow and atherosclerosis. Results at higher Sc values were wanted in order to match blood properties (Sc ranging from 1.5 x 10(5) to 6 x 10(5)). Glycerin was found to be the best viscosity modifier, although it posed some experimental problems; the presence of glycerin and sodium hydroxide results in the degradation of ferricyanide ions. The rate of degradation is directly proportional to the temperature and ferricyanide concentration. Thus, the experiments had to be performed rapidly after preparation of the solution. After optimization of the experimental conditions, a Schmidt number of about 50000 was obtained, higher than those attained previously and likely the highest Schmidt number achieved experimentally in homogeneous solutions. Averaged mass transfer in both the pipe and the bifurcation showed the same trend as those obtained previously at lower Schmidt numbers. The dependence of the Sherwood number on Sc-1/3 holds well for laminar flow up to at least Sc = 50000. The 1/3 exponent also holds in turbulent flow, measured up to a Reynolds number of 10000.