We show that volatile organic compounds (VOCs) produced by rhizospheric strainsPseudomonas fluorescensB-4117 andSerratia plymuthicaIC1270 may act as inhibitors of the cell–cell communication quorum-sensing (QS) network mediated byN-acyl homoserine lactone (AHL) signal molecules produced by various bacteria, including strains ofAgrobacterium,Chromobacterium,PectobacteriumandPseudomonas. This quorum-quenching effect was observed when AHL-producing bacteria were treated with VOCs emitted by strains B-4117 and IC1270 or with dimethyl disulfide (DMDS), the major volatile produced by strain IC1270. LC-MS/MS analysis revealed that treatment of strainsPseudomonas chlororaphis449,Pseudomonas aeruginosaPAO1 orPs. fluorescens2-79 with VOCs emitted by strain IC1270 or DMDS drastically decreases the amount of AHLs produced by these bacteria. Volatile organic compounds produced byPs. chlororaphis449 were able to suppress its own QS-induction activity, suggesting a negative interaction between VOCs and AHL molecules in the same strain. Quantitative RT-PCR analysis showed that treatment ofPs. chlororaphis449 with VOCs emitted by cells of IC1270, B-4117 or 449 itself, or with DMDS, leads to significant suppression of transcription of AHL synthase genesphzIandcsaI. Thus, along with AHLs, bacterial volatiles might be considered another type of signal molecule involved in microbial communication in the rhizosphere.