The serendipitous detection of strong antileukemic properties of guinea pig serum2 was attributed by Broom et al.3 to L-asparaginase activity, and indeed low (μM) Km bacterial asparaginases (Class 1 in revised classification4) of type II5, notably E. coli EcAII, but not type I (e.g. EcAI with mM Km6) became potent drugs in the treatment of acute lymphoblastic leukemia (ALL)7. The gene discussed is ASPG; the disease is acute lymphoblastic leukemia.