Various growth factors, hormones and proteins present in serum are presumed to be responsible for its growth-stimulating activity in culture media. However, synthetic or serum substitute media supporting cell growth are advantageous when it is necessary to standardize culture conditions, particularly when cell products are used. In this study we have evaluated and compared the effects of some commercially available serum substitute media (10% NU Serum, 10% BMS, 2% Ultroser HY, 1% ITS + Premix, 1% Nutridoma, Ultradoma, FEB100, DCCM1 and DCCM2) on growth and immunoglobulin production in different hybridoma cell lines. Six different hybrids were studied OKT3, OKT4 and OKT8 (producing monoclonal antibodies against CD3, CD4 and CD8 molecules), HB43 and HB57 (producing monoclonal antibodies against human IgG and IgM), and CRL 8019 (producing monoclonal antibodies against high-molecular weight CEA). Several parameters were evaluated, such as viability, doubling time, DNA synthesis, monoclonal antibody production and cell cycle under different culture conditions. Since not all of the hybridomas grew equally well in the same serum substitute media, one synthetic medium cannot be used for all the lines. We found that the serum-free media that best supported hybridoma growth were Nutridoma, DCCM1, DCCM2, NU Serum and FEB100.