Atonic absorption spectrophotometry was used to measure small amounts of Rb in the presence of relatively large amounts of K in plant material. Wet digestion with concentrated nitric acid provided good recoveries of Rb. A low temperature propane‐air flame and‐ a supporting electrolyte ofINHNO3+ 500 ppm Cs + 1000 ppm La were used to eliminate chemical and physical interferences of variable components of different plant parts and different plant species.