Sets of new gene sequences from human, nematode, and yeast were compared with each other and with a set of Escherichia coli genes in order to detect ancient evolutionarily conserved regions (ACRs) in the encoded proteins. Nearly all of the ACRs so identified were found to be homologous to sequences in the protein databases. This suggests that currently known proteins may already include representatives of most ACRs and that new sequences not similar to any database sequence are unlikely to contain ACRs. Preliminary analyses indicate that moderately expressed genes may be more likely to contain ACRs than rarely expressed genes. It is estimated that there are fewer than 900 ACRs in all.