Earthworm fibrinolytic enzyme component B (EFE-b) is one of three high-fibrinolytic components found in Eisenia fetida. Several crystal forms were obtained by the hanging-drop vapour-diffusion technique. Diffraction data were collected from two well diffracting crystal forms. Crystal form I diffracted to a resolution of 2.25 A but was merohedrally twinned, with space group P2(1)3, unit-cell parameters a = b = c = 122.9 A and two molecules per asymmetric unit. Crystal form II diffracted to beyond 2.06 A resolution and belonged to space group P6(3)22, with unit-cell parameters a = b = 96.4, c = 150.8 A and one molecule per asymmetric unit. Crystal form II was a true single crystal and is suitable for structure determination.