Potassium independent asparaginase has been purified from the testa of maturing seeds of Lupinus polyphyllus. The enzyme has a Mr of 71 × 103 and is composed of two subunits of Mr 35–36 × 103. Antisera raised against the purified asparaginase cross-reacted with a protein of similar characteristics isolated from the cotyledons and leaves of L. polyphyllus but no reaction was detected with extracts from the roots and nodules following Western blot analysis. Potassium dependent asparaginase was purified to a lesser extent from the testa of pea seeds and was shown to have a Mr of 61 × 103. The potassium independent and dependent enzymes appear to be distinct proteins with different immunological characteristics. The proportion of the two enzymes varies with plant species, organ and developmental age.