Low DNA Mass Ladder (patent pending) is suitable for estimating the mass (quantity) of unknown DNA samples by ethidium bromide staining (1). Prepared from a specially constructed plasmid, the ladder consists of an equimolar mixture of six blunt-ended fragments from 100 to 2,000 bp. Electrophoresis of 4 µl of Low DNA Mass Ladder results in bands containing 200, 120, 80, 40, 20, and 10 ng (470 ng total) of DNA, respectively.