To evaluate the effects of tetramethylpyraze (TPZ) on the collapsed lung during one lung ventilation (OLV), 2.4 adult patients with esophageal cancer,ASA grade Ⅰ-Ⅱ,undergoing esopha-goesophagostomy, were randomly allocated to receiving intravenous infusion with TPZ 4mg?kg~(-1) (group T,n=12) or equivalent volume of normal saline (group C,n=12) in 5 mins before onset of OLV respectively. The ultrastracture of collapsed lungat 90th min following OLV showed that in group C mitochondia swelled, the cristae disappeared, and large vecule appeared, but in group T those remained normal. As compared with those in group C,the Ca~(2+) content in erythrocyte decreased significantly 30 and 60 mins following OLV (P