Hydrophilic Streptavidin Magnetic Beads are 2 micron superparamagnetic particles covalently coupled to a highly pure form of streptavidin. The beads can be used to capture biotin labeled substrates including antigens, antibodies and nucleic acids. The strength of the biotin-streptavidin interaction coupled with the low non-specific binding of streptavidin permits captured substrates to be useful as ligands in subsequent experiments including mRNA isolation and the capture of primary or secondary antibodies