mRNA and protein expression profiles for heat shock protein 70 (Hsp70) of Babesia gibsoni (BgHsp70) exposed to either high or low temperatures, were examined by quantitative real-time reverse transcription-polymerase chain reaction and Western blotting. In the present study, a commercially available anti-human Hsp70 antibody that could recognize recombinant BgHsp70 was used. BgHsp70 was detected in the parasites cultured under standard conditions at 37 C by Western blotting and immunostaining of thin smears of infected erythrocytes. These results suggested that BgHsp70 was expressed constitutively at the erythrocyte stage. BgHsp70 levels were elevated when the parasites were incubated at 42 C for 1 hr. In contrast, its mRNA amount was decreased and its protein amount was unchanged when the parasites were incubated at 32 C for 1 hr. Moreover, the level of parasitemia of B. gibsoni incubated at either 42 C or 32 C was almost the same as that at 37 C. These results indicated that the exposure of B. gibsoni to elevated temperatures might result in increased expression of BgHsp70 and that the exposure of the intraerythrocytic parasites to decreased temperatures might not induce the overexpression of BgHsp70.