Dictyostelium discoideum is of considerable interest as an expression system for the production of proteins of high value. The cultivation of this social amoeba is not as easy as that of other common microbial expression systems. Wildtype strains grow on bacteria. Mutant strains growing on axenic media reach cell densities of 1-2 x 10(7) ml(-1) when cultivated in commonly used complex media. A totally synthetic medium formulated by Franke and Kessin (Proc. Natl. Acad. Sci. USA 74 (1977) 2157) has become popular and allows cell densities of about 3 x 10(7) Ml(-1) to be obtained. This medium (FM) is being improved mainly on the basis of the analysis of limitations with respect to amino acids. With this improved synthetic medium (SIH) cell densities in the order of 5-6 x 10(7) ml(-1) have been achieved. (C) 2003 Elsevier Ltd. All rights reserved.