The transmucosal fluxes of Na⁺ and Cl⁻ were studied in Giardia lamblia infected mice in the presence or absence of phorbol-12-myristate-13-acetate (PMA), the activator of protein kinase C (PKC) or 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine (H-7), the inhibitor of PKC or Ca²⁺-calmodulin. 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 ionophore or PMA resulted in net secretion of Na⁺ and Cl⁻ in the control group while in the infected group there was no change in the fluxes of these ions. The selective potent inhibitor of protein kinase, C, H-7, reversed the secretion of Na⁺ and Cl⁻ in infected group to absorption. The addition of PMA and Ca²⁺-ionophore together in the infected group had a partial additive effect. This study suggests that G. lamblia induced fluid secretion involves protein kinase C and further protein kinase C acts in synergism with calcium.