Trematodes such as the liver fluke Fasciola hepatica and the rumen fluke Calicophoron daubneyi are endemic throughout Europe where they tyically infect sheep and cattle. Adult fluke shed thousands of eggs which possess a tougher outer eggshell composed of cross-linked eggshell precursor (or vitelline) proteins. Fasciola hepatica usues di-tyrosine crosslinking (typcial of most trematode species) whilst the crosslinks formed in C. daubneyi eggshells appear to be different, based on histochemical data. Here, the composition of the eggshell of both species was investigated by mass spectrometry.