A comparison of codon usage in the region close to the termination codon in E. coli genes with the average E. coli codon usage shows that those codons which differ from termination codons by one base change, called pretermination codons, appear more frequently at the end of the gene. The higher frequency of pretermination codons in this region might be due to single base mutations of previously existing multiple termination codons. In addition, a comparison is made of termination codon usage, tandem termination frequency, and termination context in E. coli, H. sapiens and bacteriophage T4.