The social amoeba Dictyostelium discoideum represents an attractive host organism for the production of heterologous proteins. However, its application is seriously affected by slow growth rates as well as low maximal cell densities in the presence of axenic (liquid) media. Starting with standard complex media the influence of certain medium components was investigated. The kind and concentration of carbohydrates, the concentration of salt and ammonia and the supplementation of conditioned media were varied. These studies were performed by following cell growth in batch experiments over the whole growth cycle into the decline phase to obtain information about growth rates as well as maximal cell densities. Only maltose, glucose and a-trehalose were metabolised at significant rates. The concentration of ammonia produced correlated inversely with the concentration of carbohydrates metabolised. Under standard conditions ammonia reached concentrations of about 50 mM, most being produced during stationary phase. Ionic strength and the addition of ammonia affected the growth rate as well as the maximal cell density. Ammonia did not limit maximal cell density. D. discoideum can be cultivated in normal stirred bioreactors. A semi-empirical model is discussed for the description of the growth behaviour. (C) 2003 Elsevier Science Ltd. All rights reserved.