Cytokine mRNA expression in biopsies of Mycobacterium ulcerans-infected human tissue was investigated using real-time PCR, and the findings were correlated with the clinical stages of disease and histopathologies. A broad range of cytokine mRNAs were detected in 16 early nodules and 28 late-stage ulcers, including those for the Th1 cytokines tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) and the Th2 cytokine interleukin 10 (IL-10). IFN-gamma was strongly expressed in both nodules and ulcers, suggesting that a Th1 response begins early in the disease. There was a significantly higher expression of IL-8 and other proinflammatory cytokines in results from 32 biopsies with neutrophilia than in those from 12 biopsies without acute inflammation. Ten tissue samples containing granulomas showed high mRNA expression for IFN-gamma, IL-1beta, IL-12p35, IL-12p40, IL-15, and TNF-alpha relative to 34 tissue samples without granulomas. These results suggest that the human immune response to M. ulcerans is similar to that seen with some other mycobacteria despite the presence of the toxin mycolactone in the tissues.