The transmucosal fluxes of Na⁺ and Cl⁻ were studied in Giardia lamblia-infected mice in the presence of absence of dantrolene (1-(5(p-nitrophenyl)furfurilidene-amino) hydantoinsodiumhydrate). There was net secretion of Na⁺ and Cl⁻ in infected animals, while in control animals there was net absorption of these ions. The addition of dantrolene resulted in significant net increase in absorption of Na⁺ and Cl⁻ in control and experimental groups. Further, mouse intestinal epithelial cells were labelled with [³²P]Pi and then treated with G. lamblia trophozoites and their excretory secretory products separately. The optimum time for inositol triphosphate formation was 15 min in control enterocytes as well as in treated enterocytes. A plateau was formed at higher concentrations. Since raised inositol triphosphate levels mobilize Ca²⁺ from intracellular stores and dantrolene traps Ca²⁺ within intracellular calcium stores, the present study thus suggests that intracellular calcium stores are involved in G. lamblia-induced diarrhoea in mice.