Early diagnosis of leptospirosis of pulmonary diffuse hernorrhage type （PDH） is of crucial importance in saving patients. To develop a sensitive and specific methed for diagnosis

a genomic library of the main pathogen of PDH

L. interrogans serovar lai strain 017

was constructed with the plasmid vector PUC9. Recombinant plasmids which have hornologous fragments of pathogenic leptospires were screened from the bank. A recombinant plasmid

designated PCX7

could detect 1.7 kb fragment of strain 017

9. 0 kb of strain 601 and 30. 0 kb of strain Hebdomadis

respectively

without cross hybridization with nonpathogenic leptospires such as L. biflexa strain Patoc I and hoptonema illini. The recombinant plasmid PCX7 could detect pathogenic leptospires which are the main pathogens endemic to Sichuan Province.