Background: In 2003,we developed an ab initio program,ZCURVE1.0,to find genes in bacterial and archaeal genomes.In this work,we present the updated version (i.e.ZCURVE 3.0).Using 422 prokaryotic genomes,the averageaccuracy was 93.7% with the updated version,compared with 88.7% with the original version.Such results also demonstrate that ZCURVE 3.0 is comparable with Glimmer 3.02 and may provide complementary predictions to it.In fact,the joint application of the two programs generated better results by correctly finding more annotated genes while also containing fewer false-positive predictions.As the exclusive function,ZCURVE 3.0 contains one post-processing program that can identify essential genes with high accuracy (>90%).