Kepes and Beguin (1966) demonstrated an inhibition of induced β-galatosidase peptide synthesis by hydroxylamine (HA) without effect on messenger RNA (m-RNA) formation. The mechanism by which HA inhibits chain initiation is unclear, as is the question whether the effect is general or only specific for the β-galactosidase peptide. Experiments with E. coli strains K12 (λ) and 113-3 (a met, B12 auxotroph, Davis and Mingioli, 1950) indicated more severe inhibition of β-galactosidase synthesis by HA if glycerol, or similar metabolizable carbon sources are present in the medium. This report demonstrates that in some strains, the HA effect involves catabolite repression in addition to interference with translation of the specific m-RNA. The use of HA as a specific inhibitor of chain initiation is thus limited in such strains. © 1967.