L-Asparaginase (L-ASNase, EC 126.96.36.199) catalyzes the hydrolysis of the non-essential amino acid L-Asn to L-Asp and ammonia and is widely used for the treatment of haematopoetic diseases such as acute lymphoblastic leukaemia (ALL) and lymphomas. Therapeutic forms of L-ASNase come from different biological sources (primarily E. coli and Erwinia chrysanthemi). It is well established that the various preparations have different biochemical pharmacology properties, and different tendency to induce side-effects. This is due to different structural, physicochemical and kinetic properties of L-ASNases from the various biological sources. Understanding these properties of various L-ASNases would allow a better decipherment of their catalytic and therapeutic features, thus enabling more accurate predictions of the behaviour of these enzymes under a variety of therapeutic conditions. In addition, detailed understanding of the catalytic mechanism of L-ASNases might permit the design of new forms of L-ASNases with optimal biochemical properties for clinical applications. In this paper we review the available biochemical and pharmacokinetic information of the therapeutic forms of bacterial L-ASNases, and focus on a detailed description of structure, function and clinical applications of these enzymes.