The invention provides a method of diagnosing Mycobacterium tuberculosis infection in a human, or of determining whether a human has been exposed to Mycobacterium tuberculosis, comprising: (i) contacting T-cells from said human with one or more of (a) a peptide having the sequence shown in SEQ ID NO: 1 (b) a peptide having or comprising the sequence of at least 8 consecutive amino acids of the sequence shown in SEQ ID NO: 1 or (c) a peptide having or comprising a sequence which is capable of binding to a T-cell receptor which recognizes a peptide as defined in (a) or (b) and (ii) determining whether any of the said T-cells recognize said peptide, wherein steps (i) and (ii) are optionally carried out in vitro.
