This invention provides a method for producing a temporally paced subtracted cDNA library comprising: a) isolating temporally spaced RNAs from cells; b) generating cDNA inserts from the RNAs isolated from step (a); c) producing a temporally spaced cDNA library having clones containing the cDNA inserts generated from step (b); d) producing double stranded cDNA inserts from the temporally spaced cDNA library; e) denaturing the double stranded cDNA inserts; f)contacting the denatured double stranded cDNA inserts produced in step (e) with single-stranded DNAs from another cDNA library under conditions permitting hybridization of the single-stranded DNAs and the double-stranded cDNA inserts; g) separating the hybridized cDNA inserts from the unhybridized inserts; h) generating a cDNA library of the unhybridized inserts, thereby generating a temporally spaced subtracted cDNA library.