An IgM antibody was purified from hybridoma supernatant containing serum using a three-step purification process comprising of tangential flow filtration, anion-exchange chromatography and size-exclusion chromatography. Recovery and purity were significantly improved upon adaptation of the hybridoma to serum-free media. The process could even be simplified by omitting the initial tangential flow filtration step. Even with a two-step purification process a purity of >98% and a recovery of >60% was obtained.