DOI: http://dx.doi.org/10.5915/26-2-16366 Cell-mediated immunity (CMI) was studied in 100 patients with cancer and 20 healthy control volunteers with comparable age and sex ratios. Delayed hypersensitivity was estimated by DNCB and PPD cutaneous reactivity in vivo while lymphocyte subpopulations were estimated by peripheral blood lymphocyte (PBL), total rosette forming cells (TRFC) and active rosette forming cells (ARFC) in the peripheral blood. Purified protein derivative (PPD) and Di-nitrochlorobenzene (DNCB) cutaneous reactivity was positive in 4 percent and 64 percent respectively. TRFC values were expressed as a percentage of PBL and were found to be significantly decreased in cancer Stage I (35.5 percent; p< 0.05), Stage II (46.6 percent), Stage III (46.2 percent) and Stage IV (45 percent); the decrease in Stages II, III, and IV was insignificant as compared to the control group (51.5 percent). On the contrary, ARFC levels expressed as a percentage of PBL were significantly decreased in cancer Stage I (21.5%, p< 0.05), but significantly increased in Stage II (35.6 percent), Stage III (33.5 percent) and Stage IV (32.4 percent) as compared to control group (23.6 percent). Since DNCB cutaneous reactivity showed good immunological reserve in advancing stages of cancer in our study, a linear correlation could be established between DNCB cutaneous reactivity and ARFC levels. Since ARFC sub-population is the functionally active T-lymphocyte sub-set against malignant cells in vivo, these cells increased with proliferation of malignant cell mass in vivo, whereas PBL and TRFC levels do not exhibit significant variation. Parameters of cell mediated immunity in vitro TRFC and ARFC were significantly decreased in lymphoreticular and mesenchymal malignancies (p < 0.001). However, ARFC levels were significanlty increased in cancer of gastrointestinal tract (p < 0.05), head and neck (p< 0.05) and breast (p< 0.001) as compared to control group. Linear correlation was found with the percentage of DNCB positive reactors in each group.