The FoxP3 gene is currently the most reliable marker of suppressor regulatory T-cell activity. FoxP3 is a gene very specific to these cells. Regulatory T-cells are a sub-population of cells that have been shown to be capable of limiting immune responses to self-antigens, playing an essential role in preventing auto-immune diseases. Recent studies have demonstrated that they also serve a role in controlling many other immune responses, including inflammation, infection, allergy, graft vs host disease, organ transplantation, tumor immunity, and immunodeficiency. It is believed that this cell population may exert a "quality control" effect in a balanced immune response. In our studies, FoxP3 gene expression was measured with Real-Time PCR to assess regulatory T-cell activity. For any Real-Time PCR work, an endogenous control gene, often called a 'housekeeping' gene, must first be established. The ideal control should maintain a constant level of expression in experiments to give an accurate measure of the changes in the gene of interest. In our studies, beta-Actin proved to be the most stable and abundantly expressed housekeeping gene. Using this technique, regulatory T-cell activity was monitored in patients diagnosed with ENL (erythema nodosom leprosum). It was proposed that the medicine the patients were being treated with, known as thalidomide, was an anti-inflammatory drug therefore aiding the body's own natural defense mechanisms against the bacteria in the infection. It was discovered that the patient's immune system would call more regulatory T-cells in response to the foreign antigens threatening the body's health proving that this hypothesis was indeed true.