SYNOPSISExploratory plating tests have been carried out on a number of aqueous electrolytes based on simple ruthenium salts and nitrosyl derivatives. The nitrosyl sulphamate electrolyte emerges as the most immediately useful solution, furnishing smooth, bright deposits of ruthenium up to 0·0002 in thick over a fairly wide range of operating conditions. Cathode efficiency is always low and under preferred operating conditions is in the range of 10–20%. Deposits show internal tensile stresses in the order of 20–30 tons/in2 and fine cracks may be present at thicknesses greater than 0·0001 in. Cracking is reduced by addition of aluminium sulphate to the electrolyte. The simple sulphamate solution and an electrolyte based on reaction of sodium tetranitro-nitrosyl-ruthenate with sulphamic acid give slightly better performance than the nitrosyl-sulphamate solution when freshly prepared, but are considerably less stable in operation.