The aim of this study was the development of a simple, defined medium for the growth of laboratory and clinical isolates of Porphyromonas gingivalis. A medium was designed in which the carbon and nitrogen requirements were provided by a single protein source--bovine serum albumin. High cell yields were achieved in this medium but growth was accompanied by a heavy blackening of the cells due to the deposition of metal sulfide(s), most probably iron(II) sulfide, at the cell surface. Good growth in the absence of blackening was achieved when the iron salt in the medium was substituted with alpha-ketoglutarate. The resultant alpha-ketoglutarate/BSA medium was able to support the growth of all laboratory and clinical P. gingivalis strains examined and should prove useful in the investigation of the physiology and nutritional regulation of virulence of this organism.