A 7-μl mix containing 2.5 μg human C0t-1 DNA (Invitrogen), 2.5 μg salmon sperm DNA (Stratagene) and 500 ng whole genome fragment library was heated for 5 min. at 95°, held for 5 min. at 65° in a PCR machine and mixed with 13 μl prewarmed (65°C) 2X hybridization buffer (10X SSPE, 10X Denhardt’s, 10 mM EDTA and 0.2% SDS) and a 6-μl freshly prepared, prewarmed (2 min. at 65°C) mix of 500 ng biotinylated RNA and 20 U SUPERase-In. After 66 h at 65°C, the hybridization mix was added to 500 ng (50 μl) M-280 streptavidin Dynabeads (Invitrogen), that had been washed 3 times and were resuspended in 200 μl 1M NaCl, 10 mM Tris-HCl, pH 7.5, and 1 mM EDTA. After 30 min. at RT, the beads were pulled down and washed once at RT for 15 min. with 0.5 ml 1X SSC/0.1% SDS, followed by three 10-min. washes at 65°C with 0.5 ml prewarmed 0.1X SSC/0.1% SDS, resupending the beads once at each washing step. Hybrid-selected DNA was eluted with 50 μl 0.1 M NaOH. After 10 min. at RT, the beads were pulled down, the supernatant transferred to a tube containing 70 μl 1 M Tris-HCl, pH 7.5, and the neutralized DNA desalted and concentrated on a QIAquick MinElute column and eluted in 20 μl. We routinely use 500 ng of “pond” and “bait” per reaction but have seen essentially identical results in proportionally scaled-down 5- μl reactions with 100 ng each.