At 400 Mb, the Japanese pufferfish, Fugu rubripes, has the smallest vertebrate genome but has a similar gene repertoire to other vertebrates. Its genes are densely packed with short intergenic and intronic sequences devoid of repetitive elements. It likely has a mutational bias towards DNA elimination and is probably close to a 'minimal' vertebrate genome. As such it is a useful reference genome for gene discovery and gene validation in other vertebrates. Its usefulness in the discovery of conserved regulatory elements has already been demonstrated. The Fugu genome sequence is a good complement to genetic studies in other vertebrates.