Clinical evaluation of contact sensitization to 2, 4-dinitro-chlorobenzene [DNCB] was performed in 2 groups: group A [30 patients with non-malignant disease] and group B [30 patients with bronchogenic carcinoma]. Initial sensitization was elicited out by applying 2, 000 ug of DNCB to skin surface of the both group A and B. Subsequently a relatively weak challenge dose, 200 ug of DNCB, was applied 14 days later, showing the satisfactory results of sensitization with minimizing non-specific irritative inflammatory skin response. Delayed cutaneous hypersensitivity reactions shown by spontaneous flare phenomena appeared at the challenge site, and they were assessed 48 hours later. The reaction were graded from +1 to +4 according to the degree of flare or vesicular reaction. The results were as follows: 1. 28 cases [93%] of group A, however, only 18 cases [67%] of group B exhibited delayed cutaneous hypersensitivity reaction to DNCB contact sensitization [P<0.02]. 2. Of group A, the delayed cutaneous hypersensitivity reactions above +2 of DNCB score were 25 cases [83%], meanwhile 11 cases [37%] in group B [P<0.001]. 3. Undifferentiated carcinomas showed highest incidence of anergy to DNCB contact sensitization in the all histologic types of group B. 4. In group B, 8 [42%] of 19 cases who react to DNCB were resectable, whereas only 2 [18 %] of 11 cases who failed to react to DNCB were resectable for curative cancer surgery. These study suggests that cellular immune reaction of group B was depressed remarkably comparing with that of group A.[KTCS 1979;1:16-22]