The expression of IL-4 in a rat model of chronic pulmonary infection biofilm formation induced by Pseudomonas aeruginosa was investigated,in which SPF Wister rats were infected via trachea with 0.1 ml P.aeruginosa strain PAO579(10~9 CFU/ml)in alginate beads or the planktonic form of this bacterial strain(10~9 CFU/ml),and on 3,7 and 14 d after infection,the bacteriological and pathological changes were observed as well as the expression of the cytokine IL-4 was determined.It was demonstrated that the count of CFU per lung tissue in case of bacteria in alginate beads was significantly higher than that of bacteria in planktonic form,with more severe gross pathologic changes and inflammatory reactions in the alginate bead group in comparison with that of the planktonic forms(P=0.002,P=0.004 and P=0.002,respectively).In addition,the expression of IL-4 in the alginate bead group was also higher than that in the planktonic form(P=0.02,P=0.02 and P=0.022,respectively).A positive corre- lation between the level of IL-4 expression and the gross lung pathology in alginate bead group existed as demonstrated by simple regression analysis(r=0.78,P<0.02).It is concluded that the chronic pul- monary infection with biofilm formation induced by P.aeruginosa tends to have the priority to the Th2 immune response. The expression of IL-4 in a rat model of chronic pulmonary infection biofilm formation induced by Pseudomonas aeruginosa was investigated, in which SPF Wister rats were infected via trachea with 0.1 ml P. aeruginosa strain PAO579 (10-9 CFU / ml) in alginate beads or the planktonic form of this bacterial strain (10-9 CFU / ml), and on 3,7 and 14 d after infection, the bacteriological and pathological changes were observed as well as the expression of the cytokine IL-4 was determined. It was demonstrated that the count of CFU per lung tissue in case of bacteria in alginate beads was significantly higher than that of bacteria in planktonic form, with more severe gross pathologic changes and inflammatory reactions in the alginate bead group in comparison with that of the planktonic (P = 0.002, P = 0.004 and P = 0.002, respectively). In addition, the expression of IL-4 in the alginate bead group was also higher than that in the planktonic form (P = 0.02, P = 0.02 and P = 0.022, respectively) .A positive correlation between the level of IL-4 expression and the gross lung pathology in alginate bead group existed demonstrated by simple regression analysis (r = 0.78, P <0.02) .It is said that the chronic pul monary infection with biofilm formation induced by P .aeruginosa tends to have the priority to the Th2 immune response.