Few data are available for diffusion coefficients measured in industrial copper electrolytes. In the present work the influence of copper concentration (19.9-58.1 g dm(-3)), temperature (20-60 degrees C) and concentrations levelling agents i.e. animal glue (0-5 mg dm(-3)) and thiourea (0-5 mg dm(-3)) on diffusion coefficients of copper was studied in industrial copper refinery electrolytes. Chronoamperometry at ultramicroelectrodes was used as an electrochemical technique. Apparent bulk diffusion coefficients were calculated on the basis of the theory of electrochemical nucleation on disc-shaped ultramicroelectrodes. Increasing copper concentration decreased the apparent bulk diffusion coefficient of copper and diffusion coefficients followed the Arrhenius temperature relationship. The experimental activation energy was 26.8 kJ mol(-1). The influence of levelling agents on diffusion coefficients was not strong in the studied concentration range of animal glue and thiourea.