In this work, we report the existence of enhanced concentrations of IL-2 (Th1 cytokine), TNF-alpha (mainly a Th1 cytokine), IL-12p40, a strong delayed type hypersensitivity response, and the absence of a serum-specific antibody response (IgG or IgE) in patients with active chiclero's ulcers. There was a low serum concentration of IL-6 (a Th2 cytokine) that was further reduced once patients healed following antimonial therapy (i.e., 4 months after treatment started). There was an absence of serum IL-4 (a Th2 cytokine) in patients before and after healing. The serum content of nitric oxide, transforming growth factor-beta1, and IL-12p70 in patients with progressive chiclero's ulcers was not different from that of controls. Patients had an alteration in blood-cell counts and showed a poor T cell proliferation after in vitro stimulation with Leishmania mexicana gp63. We concluded that patients with progressive chiclero's ulcers develop a Th1 type of response at this stage of the disease which correlates with increases in circulating eosinophils and B cells and a reduction of circulating CD8(+) T lymphocytes.