An enzyme that catalyzes the hydrolysis of both glutamine and asparagine has been purified to homogeneity from extracts of Pseudomonas acidovorans. The enzyme having a ratio of glutaminase to asparaginase of 1.45:1.0 can be purified by a relatively simple procedure and is stable upon storage. The glutaminase-asparaginase has a relatively high affinity for-asparagine (K,,, = 1.5 x 10-5 M) and L-glutamine (K,, = 2.2 x 10-5 M) and has a molecular weight of approximately 156,000, the subunit molecular weight being approximately 39,000. Injections of the enzyme produced only slight increases in the survival time of C3H/HE mice carrying the asparagine-requiring 6C3HED Gardner lymphoma and of white Swiss mice carrying the glutamine-requiring Ehrlich lymphoma.'