The electrochemical technique has been used to measure mass transfer rates between nickel surfaces and the ferro-, ferricyanide electrolyte solution flowing in a 38 mm IT) circular pipe. Data for one smooth and six rough surfaces are reported. The surfaces were Fabricated by a novel electroplating technique. The rough surfaces had V-shaped grooves transverse to the flow direction, 76-1500 mu m deep. The experiments covered the Reynolds number range of 500-350 000; Schmidt numbers varied from 550 to 4720. Friction factors were measured for 4000 < Re < 240 000. The results are correlated by the mass transfer similarity function. Transfer enhancement depends on groove size and frequency and on flow conditions. Rates higher than three times the corresponding smooth surface values were observed. A mass transfer efficiency index is proposed, relating enhancement to frictional losses.