Mo-clay was used by German doctors to treat injured soldiers' wounds during the First World War. Today, there are anecdotal cases of mo-clay being beneficial for patients suffering from psoriasis, a chronic, inflammatory disease. There are several histological features in the psoriatic skin, including acanthosis, hyperkeratosis, pararkeratosis and a loss of granular layer. Mo-clay is a unique marine deposit, an Eocene clayed diatomite. It was formed 54 million years ago from deposits of single-celled algae along with clay minerals and volcanic ash. The major elements are silicon, aluminium and iron. It is found in Denmark and Germany. As mo-clay had been used to treat wounds, it was tested for antibacterial activity. Mo-clay did not show any anti-bacterial activity against a battery of Gram-positive and -negative bacteria. Mo-clay showed stimulation of cell proliferation at concentrations 39 – 78 µg/ml in splenic mouse lymphocytes, and at 156 µg/ml in HaCat cells, whereas an inhibition of proliferation was observed at 313 µg/ml. Mo-clay was tested for anti-psoriatic activity in vivo using the mouse tail test [1]. This model can be used to investigate agents for effect on psoriasis, since the adult mouse tail has regions of both orthokeratosis and parakeratosis. Mo-clay induced orthokeratosis and showed a significant increase in epidermis thickness. The results suggest that mo-clay may have anti-psoriatic effects.