The present study reports an improved PCR-based technique that allows quick and effective screening of cDNA libraries. First

the cDNA library was arrayed as follow: about 3 X 10’ cDNA clones were multiplied as individual plaques on solid medium in 24-well culture dishes at 1 200 plaque forming units per well. The phage suspension of each well was transferred to an individual microcentrifuge tube in 72-tube box. Then

box pool

row pools and column pools were set up that respectively represent a 72-tube box

rows and columns within the box. To screen a specific target cDNA

primers specific for novel ESTs ob- tained in our laboratory were employed to conduct PCR in a hierarchy mode. PCR began with the box pools

resulting in the identification of some Positive box pools. Then PCR went down to the row and col- umn pools of the positive box. The intersection of the positive row （s） and column （s） revealed the candi- date positive tubes. The specificity of PCR products were meanwhile checked by restriction enzyme diges- tion. Finally

hybridization was carried out to get single specific cDNA clomes from the positive tubes. This PCR-based technique features high specificity

high efficiency and less-cost in large-scale cDNA library screening. Our initial implementation of the technique resulted in the isolation of three longer different cD- NA clones from a human fetal brain cDNA library. Thus this improved technique can serve as an alterna-tive to the time-consuming and laborious conventional hybridization-based method for screening cDNA li-brary.