SUMMARY Prototrophic ‘revertants’ of methionine-requiring methionyl-tRNA synthetase mutants (metG) of Salmonella typhimurium were examined following an observation that some of them excreted methionine. A number were found to be phenotypically indistinguishable from a class (metK) of methionine regulatory mutants. The mutations causing reversion, like metK mutations, were located between a serine (serA) and a methionine (metC) structural gene on the linkage map, and it was concluded that the ‘suppressors’ were metK mutations. The ability of independently isolated metK mutations to cause suppression of metG mutants was tested and was apparently related to their ability to cause methionine overproduction. A second kind of methionine regulatory mutation (metJ) also caused suppression, while a metA (homoserine-O-transsuccinylase) mutation leading to feedback insensitivity failed to do so. Spontaneous metG revertants due to secondary metJ mutations were rare, and none due to secondary metA mutations was detected.