Abstract: The relationship between the different ages (3、10、22weeks) and histamine - induced airway reactivities was studied in conscious and unrestrained guinea pigs. The result showed that the difference of histamine - induced airway reactivities between 3 and 10 week - old animals was not significant (P＞0.05),but the response to histamine in 22 week - old animals was reduced significantly as compared with those in 3 and 10 week - old guinea pigs (P＜0.01). And it was suggested that 7～10 week - old guinea pigs may be the most suitable for asthma experiment.