The uptake of aliphatic amides by P. aeruginosa 8602 was studied by using l-Cl4-acetamide and 1-C14-N-acetylacetamide (a non-metabolizable analogue). l-Cl4-acetamide was accumulated by the wild-type strains and by an amidase-negative mutant. The maximum ratio of internal to external concentration measured was 100:1. l-Cl4-N-acetylacetamide was concentrated by the wild-type strain and the maximum ratio of internal to external concentration measured was 80:1. No difference was detected in amide uptake as between induced and non-induced cultures of the wild-type or mutant strains. It is concluded that the organism possesses a consti-tutative permease for these amides. Cyanoacetamide had no significant effect on N-acetylacetamide accumulation by the wild-type strain at concentrations which repressed amidase synthesis. Repression of ami-dase synthesis by amide analogue repressors is therefore not due to inhibition of amide uptake by the bacteria.