The antiparasitic activity of racemic albendazole-sulphoxide (Ricobendazole = racRBZ) and its ( ) and (−) enantiomers was tested in an ex vivo murine model for Trichinella spiralis infection. Larvae were isolated from the muscle of infected mice and exposed to concentrations between 0.01 and 1 μg/ml of the racemic mixture or to each of its enantiomers. The activity of each compound was then assayed by measuring the ability of the treated larvae to infect naive mice (larval viability). At a concentration of 0.5 μg/ml, all 3 compounds were highly effective in reducing the viability of the larvae, achieving reductions of 91.26% (racRBZ), 96.7% ( ), and 89.2% (−), when compared with untreated controls. At lower concentrations (0.1 μg/ml), only treatment with ( )RBZ rendered a significant reduction in larval viability in comparison with controls (84.3%; P < 0.01), whereas at 0.01 μg/ml, none of the compounds altered larval viability (P > 0.05).