The matrix metalloproteinases (MMPs) are important in tumour cell invasion and metastasis in many common cancers. However, relatively few studies have investigated the role of MMPs and their inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), in leukaemia cell invasion. This study examined two leukaemia cell lines, K562 and HL-60 and showed that the K562 cell line was four times more invasive than the HL-60 cell line. The expression of MMP-2, matrilysin (MMP-7), MMP-9. TIMP-1, TIMP-2 and TIMP-3 was analysed. Both cell lines produced similar amounts of MMP-2, MMP-9 and TIMP-2. The K562 cells expressed more TIMP-1 than the HL-60 cells and neither cell line expressed TIMP-3. Interestingly, only the K562 cells expressed matrilysin suggesting a potential role for matrilysin in leukaemia cell invasion. in vitro invasion assays performed in the presence of a matrilysin blocking antibody showed a 40% reduction in invasive ability. This data suggests that matrilysin plays an important role in leukaemia cell invasion.