This study compares the relative capacities of four serum-free media to support growth and MAb production for three mouse hybridoma cell lines. A 10% foetal bovine serum-Iscove's medium served as the control medium. The four serum-free media included Ventrex HL-1, Iscove's with 2% Ultroser HY, HybriMax DME/F12, and KC 2000. Ultroser HY supported the best cell growth of the serum-free media. The greatest antibody yields for hybridoma TDIII,IIIBB2 were observed with Ultroser HY and KC 2000 whereas hybridoma TDII,IAA11 secreted the most MAb in Ultroser HY but only 0-0.04 mg/ml with the other serum-free media. Serum-free media were not suitable for MAb production by hybridoma BGII,VF9/2D. Serum-free media never supported growth levels and MAb yields as high as serum-supplemented media. MAb production and growth in serum-free media were variable and dependent on the specific hybridoma cell line cultured.