As-p18 is a fatty-acid-binding protein from the parasitic nematode Ascaris suum. Although it exhibits sequence similarity to mammalian intracellular fatty-acid-binding proteins, it contains features that are unique to nematodes. Crystals were obtained, but initial diffraction data analysis revealed that they were composed of a number of microdomains. Interpretable data could only be collected using a microfocus beamline with a beam size of 12 8 m.Instituto de Investigaciones Bioquimicas de La Plata