This method for determination of Rb+ in human plasma and erythrocytes by graphite-furnace atomic absorption spectrophotometry has a sensitivity of 29 nmol/L for plasma, 12 nmol/L for erythrocytes. The detection limit is 24 nmol/L for plasma, 4.8 nmol/L for erythrocytes. This assay is approximately 30-fold more sensitive than previously reported techniques involving atomic absorption spectrophot...