Experimental contact dermatitis has been induced in 2,4 dinitrochlorobenzene (DNCB) sensitized guinea pigs. The developing dermal infiltrate was excised and the infiltrating cells were obtained by mechanical extraction alone as well as by the combination with collagenase and elastase treatment. The most viable cells appeared in the elastase and mechanically extracted samples and the least in those subjected to mechanical treatment alone. The most cells in the enzyme-treated samples were present 24 h after re-exposure of the sensitized animals to DNCB consisting mainly of lymphocytes and of polymorphonuclear granulocytes. The optimum conditions for the action of enzymes including optimum duration of the treatment, buffer milieu, aspecific proteolytic effect on foreign substrate and action on T and B cell receptors have been elaborated. It was concluded that 80 min of collagenase treatment with gentle mechanical extraction under specified conditions does not affect any measurable immunologic properties of the liberated cells resulting in the second best yield. A comparison of these data with earlier reports and their significance is being discussed.