Synthetic organic pesticides, such as chlorinated hydrocarbons and organophosphorous and carbamate compounds, are widely used for the control of pests and vectors in spite of the fact that these pesticides are now causing serious environmental hazards (1-4). The search goes on for pesticides of plant origin because of their rapid biodegradability. However, to date, only a few pesticides of plant origin (pyrethroids, nicotinoids, and rotenoids, etc.) are available. This is a pioneer report on the molluscicidal properties of the latex of Euphorbia royleana Boiss, a cactus-like plant, which is extremely hardy and is abundantly found throughout India; it can be planted by sowing a piece of the stem about 5 cm in soil. Water requirement is very little, and fertilizers are not needed for its growth. It has a quick knockdown action and causes high mortality of the snail Lymnaea acuminata, the intermediate host of liver flukes, Fasciola hepatica and Fasciola gigantica (5). In the present paper, we report on the antiacetylcholinesterase effect of the latex of E. royleana on the nerve tissue acetylcholinesterase of the snail L. acuminata.