Abstract Only a few prokaryotic or eukaryotic enzymes are known to consist of a tandem-repeat structure. This report describes a common hexapeptide-repeat theme in four Escherichia coli transferases and in four less-characterized bacterial proteins. The proteins are the Ssc protein of Salmonella typhimurium (25), UDP-N-acetylglucosamine acyltransferase of E. coli (24), the hypothetical proteins Tms of Bacillus subtilis (23) and Yglm of E. coli (22), succinyldiaminopimelate aminotransferase of E. coli (14), serine acetyltransferase of E. coli (13), NodL of Rhizobium leguminasorum (13), and thiogalactoside acetyltransferase of E. coli (8) (number of repeats indicated in parentheses). In UDP-N-acetylglucosamine acyltransferase, the repeats constitute 55% of the total protein. Each hexapeptide repeat of the eight proteins starts with Ile, Leu, or Val. Position b is occupied by Gly, position d by Gly, Asn, or Asp, and position e by Val or Ala in 52%, 54%, and 56% of the hexapeptide repeats, respectively.