Dictyostelium discoideum was immobilized by cultivation on inorganic porous matrices consisting of broken pumice or a ceramic catalyst carrier (CeramTec) to produce human soluble Fas ligand (hFasL). These supports were actively colonized by D. discoideum reaching cell (number) densities 10-20 times higher locally than those observed in suspension culture under similar conditions. In repeated batch or continuous operation, hFasL productivities of up to 15-25 mug h(-1) s l(-1) pore volume were attained. The immobilized cell densities and hFasL productivities could be kept constant for a long period of time by repeated renewal or continuous feeding of complex or synthetic medium.