In experiment 1, zebrafish were exposed to 0.1-600 nM Cd in order to determine if the apical uptake of Cd from the water into the branchial epithelial cells and influx of Cd to the circulatory system follow saturation kinetics, and if these processes are affected by Zn. In two other experiments (experiments 2 and 3) , the influence of Zn on the apical uptake and influx were studied in the lower range of Cd concentrations (0.1-30 nM) , in order to detect effects at more environmentally relevant Cd concentrations. Experiments 2 and 3 were designed to determine if the results were repeatable in different exposure scenarios.