Work is frequently carried out to control lichens and algae on stone in Japan, but it has not been systematically published. In this article, work on three types of stone objects is reported. The first object, of tuffaceous sandstone (1850 AD) was covered with caloplaca sp. and endocarpon sp. The parts affected were covered for 24 hours with cotton wool soaked in formalin. The second example, of pyroxene-andesite, was dated 1711 AD. Biological growth included the lichen lepraria sp. and some green algae. The third example was of the kofun period (5-6th century) and was Hornblende andesite. The green algae chlorella was found in three places. The second and third objects were treated with ac-322; it was applied to the lichens and green algae for 24 hours, then all the growth was brushed away. Photographs.