OBJECTIVE: To determine whether tuberculin skin testing (TST) is associated with an increase in human immunodeficiency virus (HIV) viral load, and to examine the effect of TST on anti-mycobacterial immune responses. DESIGN: A nested cohort study of HIV-1-infected adults. METHOD: Forty-two participants (21 TST-positive and 21 TST-negative) from a larger cohort were recruited to the study. Blood was collected for CD4+ T-cell count, whole blood was cultured, and plasma saved for viral load. These measurements were taken before, 3 days after, 3 months after, and 3 months plus 3 days after TST. Cytokine responses to culture filtrate proteins (CFP) of Mycobacterium tuberculosis and phytohaemagglutinin (PHA) were examined in the whole blood assay. RESULTS: Twenty-nine participants attended all four visits. No statistically significant change in viral load, CD4+ T-cell count, or cytokine response to PHA was observed at any visit. However, TST was associated with a transient increase in the interferon-gamma response to CFP and a lasting increase in the interleukin-5 response to CFP. CONCLUSION: There appeared to be a systemic effect of TST on the anti-tuberculosis immune response.