Xing and Xu (Acta Cryst. (2003) D59, 1816-1818) describe the crystallization of the PX domain of cytokine independent survival kinase in ammonium sulfate. Optimization of the crystallization seemingly involved the subtle manipulation of several crystallization variables, including using drop ratios (1:2 drop ratio), the removal of DTT to allow crystal growth after nucleation, as well as the substitution of sodium malonate for ammonium sulfate. The authors reported the sodium malonate dramatically increased the reproducibility of the crystals and also acted as a good cryoprotectant. Crystals grown from 2.0 M sodium malonate could be cryo protected directly from the drop. The crystals grown in sodium malonate were more resistant to physical shock compared to those grown in ammonium sulfate.