The early stages of the shell regeneration in Helix pomatia have been studied by electron microscopy. Within 1 hour after the removal of a piece of shell, minute crystals of CaCO3 appear in the injured area. Electron diffraction study showed these crystals to be aragonite. Calcite crystals were also present at later stages of regeneration (after 3 hours) as shown by polarizing microscope and X-ray diffraction. Vaterite was found in 1 of 12 cases. Spherulites were observed in regeneration at the shell edge but not elsewhere.