It is known from the literature that the circulating levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) are elevated in heart failure and idiopathic dilated cardiomyopathy (IDC). Few convincing data are available on the production of cytokines in hypertrophic cardiomyopathy (HC). The levels of circulating IL-6, the soluble form of the IL-6 receptor (sIL-6R), and TNF-alpha in 19 patients with HC, 31 patients with IDC, and 20 healthy subjects (control group) were examined and compared with their clinical parameters. The levels of TNF-alpha and circulating IL-6 proved to be elevated in the sera of patients with IDC. In contrast, the level of TNF-alpha was not elevated in HC, although the levels of IL-6 and sIL-6R were significantly higher than those in the sera of patients with IDC. Although elevated levels of IL-6 may correlate with the extent of left ventricular dysfunction in IDC, the markedly elevated IL-6 levels did not correlate with left ventricular function in HC. The markedly elevated TNF-alpha levels in IDC were associated with the elevated IL-6 levels, probably because of an inflammatory process and/or heart failure. In contrast, in HC, in which the New York Heart Association functional class was actually good, the even higher IL-6 and sIL-6R levels were not associated with a TNF-alpha elevation. In HC, the IL-6 and sIL-6R elevations were due to another mechanism, probably by way of the cardiotrophin-associated gp130 receptor. The sources of IL-6 production in HC are not clear yet.