A method for the routine determination of the Tamm and Horsfall glycoprotein in human urine is presented. The method is based on quantitative electroimmunoassay. It was demonstrated that the solubility of the Tamm and Horsfall glyco-protein was dependent on urinary ionic strength and pH. To minimize these variables all urines were buffered to pH 5.5 and then preincubated at 37° C in 0.3% sodium dodecyl sulphate. This procedure solubilized and maintained the Tamm and Horsfall glycoprotein in solution. Excess sodium dodecyl sulphate was removed by gel filtration before the quantities of the Tamm and Horsfall glycoprotein were determined by electroimmunoassay. The method is simple, reproducible, has high precision and compares favourably with earlier published methods for the determinations of the Tamm and Horsfall glycoprotein.