The ability of 2,4,6 trinitrobenzenesulfonic acid (TNBS)-induced regulatory cells to modulate the generation of contact sensitivity (CS) to picryl chloride has been studied. We have confirmed that such suppressor cells can modulate CS and have extended these observations to demonstrate that suppressor factors, liberated by suppressor cells in supernatants, can limit the generation of CS. We have also confirmed that hapten-coupled membrane products can induce tolerance to PCl. The investigation of the properties of the suppressor factors has revealed that they are hapten-specific and bear H2 coded specificities.