Genetic systems of salicylate catabolism were studied in 75 strains of fluorescent pseudomoriads and in 30 exogenously isolated SAL plasmids. All exogenously isolated SAL plasmids were found to contain the classical nahG gene in combination with the genes of the meta-pathway of catechol cleavage. In most studied strains, salicylate catabolism was controlled by the chromosomal genes, the nah Ugene being the key gene ofsalicylate utilization and subsequent catechol cleavage occurring via the ortho-pathway. It is suggested that the nah U-like sequences play a key role in occurrence of the Sal+ phenotype in strains degrading salicylate, but not naphthalene.