Abstract
Pre-reassociation of human clone probes, containing dispersed highly repeated sequences, (e.g. Alu and KpnI families), with a large excess of sonicated total human DNA allows signal from single and low copy number components to be detected in transfer hybridisations. The signal from non-dispersed repeated sequences is reduced to single copy levels. The procedure, which is simple and quick, is illustrated using model combinations of well characterised cloned probes, and is applied to a sample of randomly chosen cosmid clones. A theoretical assessment is presented which may be useful to those wishing to use this procedure.