A study was carried out on the molluscacidal action of agave (Agave legrelliana) on the mollusk Biomphalaria havanensis, host of Schistosoma. Different concentrations of the plant's juice extract were tested to determine lethal doses. 3 experimental series were carried out using 144 mollusks in each. LD50 = 0.14 mL/L and LD90 = 0.47 mL/L were determined using the "probilog" computerized program. The regression equation was Y = 5.29 + 2.53 in X. Density, pH, liquid content and absorbance of the juice were determined. The stability of the A. legrelliana juice extract was compared using LD90 and it was observed that its effectiveness was reduced after long storage periods. The results attained were very encouraging since large volumes of water abounding in intermediate host mollusks can be treated with small quantities of juice at the same time that the toxicity which might be introduced by products of chemical origin is reduced.