To study the effects of heroin on changes of weight,behavior and expression of KGF,c-Fos and Bax in the lungs of developing filial mice,48 mice at the eighth day of pregnancy were divided into 4 groups and injected with different concentrations (0,1.0,1.5 and 2.0 g/L) of heroin in 0.2 ml saline in the morning and afternoon until the birth of filial mice.Changes of weight and behaviour were observed and expression of KGF,c-Fos and Bax was detected by immunohistochemistry combined with stereological semi-quantitative methods in the lungs of 15-day embryos,and filial mice 1 d,7 d and 15 d after birth.Results showed that heroin influenced behaviour of the developing mice.The weight of filial mice of the experimental groups was lower than that of the control group at different developmental stages,and the expression intensity of KGF,c-Fos and Bax in the lungs of filial mice significantly increased (P<0.01 or P<0.05).However,the expression of KGF,c-Fos and Bax decreased gradually in the lungs of filial mice with the development.Thus,heroin significantly affects the weight and behavior,and damages the lungs in filial mice,the latter might be correlated with the increased expression of KGF,c-Fos and Bax.