A submersible electrochemical probe for in situ monitoring of trace chromium is described. The new flow probe relies on the coupling of an ultrasensitive adsorptive–catalytic stripping voltammetric procedure with a submersible operation. Such in situ monitoring involves a continuous delivery of an internal (ligand–catalyst, DTPA–NO₃^–) reagent solution, a microdialysis collection of the target chromium ion, transport of the Cr–DTPA complex and nitrate-ion catalyst to the working-electrode compartment and adsorptive–catalytic stripping detection of the complex. The optimization of various parameters resulted in a detection limit of 0.10 µg l^–1 (with 10 min accumulation), good precision and stability (RSD 6% for n=80 at 25 µg l^–1 chromium) and a rapid response to sudden changes in the chromium level. A stable response was obtained for both Cr(VI) and Cr(III) species. The attractive performance of the submersible probe holds great promise for environmental and industrial monitoring.