The method, protocol describes a technique of the preparation of subtracted cDNA probes by hybridization to an mRNA driver, followed by purification of the single-stranded radiolabeled cDNA by hydroxyapatite chromatography.  Before preparing the probe, it is a good idea to have filters (which contain the cDNA library to be screened) ready to hybridize.

Protocol: Synthesis of Radiolabeled, Subtracted cDNA Probes Using Oligo(dT) as a Primer Protocol