Abstract: An essentially pure and stablized antibody preparation comprising IgM antibodies having a purity greater than about 98% by weight and a nucleic acid content of less than about 200 pg per mg IgM. In one embodiment IgM antibodies from a monoclonal source are subjected to ion exchange and size exclusion chromatography at an alkaline pH to yield a purified IgM having a nucleic acid content of less than 10 pg/mg IgM, preferably less than about 4 pg/mg IgM. A highly purified and stabilized preparation of anti Pseudomonas aeruginosa antibodies is disclosed. The removal of nucleic acids is assured by subjecting the antibody source to at least one and preferably two low pH precipitation steps. In a very preferred embodiment, ion exchange and/or size exclusion chromatography is used to remove any residual nucleic acids.