The genome of the lower eukaryote Dictyostelium discoideum comprises six chromosomes. Here we report the sequence of the largest, chromosome 2, which at 8 Mb represents about 25% of the genome. Despite an A+T content of nearly 80% the chromosome encodes 2,799 predicted protein coding genes and 73 tRNA genes (http://genome.imb-jena.de/dictyostelium/chr2/Chr2map.html and http://www.uni-koeln.de/dictyostelium/chr2/index.shtml). This gene density, about 1 gene per 2.6 kb, is surpassed only by Saccharomyces cerevisiae (one per 2kb) and is similar to that of Schizosaccharomyces pombe (one per 2.5 kb). If we assume that the other chromosomes have a similar gene density, we expect around 11,000 genes in the D. discoideum genome. A significant number of the genes show higher similarities to genes of vertebrates than to those of other fully sequenced eukaryotes. This analysis strengthens the view that the evolutionary position of D. discoideum is located prior to the branching of metazoa and fungi but after the divergence of the plant kingdom, placing it close to the base of metazoan evolution.