An ion-pair reversed-phase partition high-performance liquid chromatography-spectrophotometric method is described for the determination of aluminum in human serum, based on its complexation with 2,2'-dihydroxyazobenzene. The chelate is separated on C18-bonded silica packing by using an aqueous methanol mobile phase containing tetrabutylammonium bromide and is detected with 0.005 AU full-scale at 510 nm. The proposed system offers a simple, sensitive, and selective method. The detection limits defined as twice the standard deviation of the blank signal, are 0.2 micrograms L-1 in pure solution and 6 micrograms L-1 in serum. The sample solution is prepared from 0.4 mL of serum after protein precipitation with hydrochloric acid and methanol. There was good agreement between the values obtained by this method and graphite furnace atomic absorption spectrophotometry. The aluminum concentrations in 121 patients on hemodialysis were 6-201 micrograms L-1.