Objective To study the biological indices and their significance of e xternal dryness injuring the lung.Methods Totally 99 SPF Kunming mice were randomized into normal temperature and humidity group

warm-dryness group

and cool- dryness group with 33 in each.The models were made under the simulated condition of "temperature-relative humidity-wind" based on literature.On the 6th

12th

and 18th day after treatment

the pathological cnanges of the trachea

lung

and the ultrastructure of type Ⅱ alveolar cell （ATⅡ） were observed

and the levels of respiratory mucopolysaccharide （RM） and dipalmitoyl phosph atidyl choline （DPPC） were detected.Results Compared w ith the normal temperat ure and humidity group

squamous metaplasia and ciliated defect of tracheal epit helia

tracheal mucous metaplasia accompanied with infiltration of infla mmatory cells

pulmonary alveolar congestion

and pulmonary emphysema were showe d on the 6th and18th day in the warm-dryness group and cool-dryness group.The e lectrion microscopy observation showed that in the warm-dryness group and coo l-dryness group there was reduction of ATⅡ microvilli.The reduction of RM in both groups was significant on the 12th day （P<0.05）

and the content of DPPC was continuously decreased from the 6th day to the 18th day （P<0.05 or P<0.01）.Conclusion The tr acheal pathological changes and ultrastructural abnormality of pulmonary respira tory mucosa AT II caused by external dryness can be taken as the basic histopath ological indices of external dryness injuring the lung

and the detection of RM and DPPC can be taken as its functional biological indices.