The aim of the study is to characterize the type of immune response in benign prostatic hyperplasia (BPH) tissue. BPH tissue–derived T cells (n = 10) were isolated, activated (PMA + ionomycin), and analyzed for intracellular reactivity with anti–IFN-γ and IL-2, -4, -5, -6, -10, and -13, as well as TNF-α and -β by four-color flow cytometry. Lymphokine release was tested using Th1/Th2 cytokine bead arrays. The amount of IFN-γ and IL-2, -4, -13, and TGF-β mRNA expressed in normal prostate (n = 5) was compared with that in BPH tissue separated into segments with normal histology (n = 5), BPH histology with (n = 10) and without (n = 10) lymphocytic infiltration, and BPH nodules (n = 10). Expression of lymphokine receptors was analyzed by immunohistology, flow cytometry, and RT-PCR. We found that 28 ± 18% of BPH T helper cells were IFN-γ+/IL-4− Th1 cells, 10 ± 2% were IFN-γ−/IL-4+ Th2, and 12 ± 6% were IFN-γ+/IL-4+ Th0 cells. In relation, cytotoxic and double-negative BPH T lymphocytes showed a slight decrease in Th1 and Th0 in favor of Th2. In double-positive BPH T lymphocytes, the trend toward Th2 (35 ± 15%) was significant (Th1: 12 ± 7%; Th0: 5 ± 4%). Lymphokine release upon stimulation was found in the case of IL-2, IL-5, IFN-γ, and TNF-α > 4 μg; of IL-4 > 2 μg; and of IL-10 > 1 μg/ml. Expression of lymphokine mRNA in tissue was increased (2- to 10-fold) in infiltrated BPH specimens with and without BPH histology. The infiltrated BPH specimens with normal histology differed from those with BPH histology, most evident by the significant decrease in IFN-γ and the increase in TGF-β mRNA expression. Infiltrated BPH specimens with BPH histology expressed significantly more IFN-γ (5-fold), IL-2 (10-fold), and IL-13 (2.8-fold) when compared with noninfiltrated BPH specimens. BPH nodules, however, showed the highest level of expression of IL-4 and IL-13, with only intermediate levels of IFN-γ and very low levels of IL-2 mRNA. Immune response in histologically less transformed BPH specimens is primarily of type 1, whereas in chronically infiltrated nodular BPH and especially within BPH nodules, it is predominantly of type 0 or type 2.