Under laboratory conditions, latex from Euphorbia splendens has shown promise as a plant molluscicide for control of Biomphalaria species, intermediate hosts for Schistosoma mansoni. The purpose of this study was to evaluate its efficiency under field conditions. Application of filtered latex at 12 ppm to one stream in an endemic rural area in Minas Gerais state, Brazil, in September 1995, did result in a reduction in snail density as compared to an untreated stream but the snail population recovered quickly. However, two applications with a two-week interval of unfiltered E. splendens latex at 5 ppm in November 1996 in the same stream resulted in complete disappearance of B. glabrata and snails did not reappear until the 14th month after the applications. In the control stream, without treatment, the snails were found during all months. Laboratory studies confirmed that unfiltered latex is a more potent molluscicide than filtered latex. Considering the advantages of the latex such as its low toxicity to other aquatic animals and its photobiodegradability, as well as the simple method of application, this natural product is promising as an effective molluscicide.