The development of media free of serum and animal or human proteins is of utmost importance for increasing the safety of biologicals produced for therapy and vaccination. In order to reduce the risk of contamination, we have modified the serum free medium MDSS2, a very efficient serum free medium for the production of various biologicals including experimental vaccines using different cell lines (Merten et al., 1994), by replacing the animal derived products by plant extracts. The new serum and animal protein free medium (MDSS2N) can be efficiently used for biomass production of various cell lines. These cells grow equally well or better in this new serum-free medium than in the old formulation (MDSS2):* BHK-21/BRS cells, adapted to MDSS2N, showed an overall specific growth rate of 0.0197 h-1 (mu_max = 0.0510+/-0.0058 h-1), whereas those cultivated in MDSS2 grew with an average specific growth rate of 0.0179 h-1 (mu_max = 0.0305+/-0.0177 h-1).* Vero cells grew with an average specific growth rate of 0.0159 h-1 and 0.0153 h-1 in MDSS2 and MDSS2N, respectively. Very similar growth rates were obtained in microcarrier cultures in stirred tank reactors: the specific growth rates were 0.0161 h-1 and 0.0166 h-1 for MDSS2 and MDSS2N cultures, respectively.* For MDCK cells, when cultured on microcarriers in bioreactors, a higher average specific growth rate was observed in MDSS2N than in MDSS2; values of 0.0248 h-1 and 0.0168 h-1, respectively, were obtained.The capacity of MDSS2N to support the production of different viruses was equally evaluated and it could be established that for certain viruses there are no or insignificant differences between MDSS2N and MDSS2 (influenza and polio virus), whereas, the production of rabies virus is somewhat reduced in MDSS2N when compared to MDSS2. The use of MDSS2N for cell culture and the production of various viruses is discussed.