Tissue inhibitor of metalloproteinase (TIMP) has been reported to inhibit tumour invasion through an inactivation of matrix metalloproteinase (MMP) both in vitro and in vivo. Among the TIMP family, TIMP-1 possesses not only proteinase inhibitory activity but also a growth-promoting function. However, the significance of the expression of TIMP-1 in human gastric carcinoma tissue has yet to be clarified. In 50 examined cases of gastric carcinoma, 44 (88%) cases showed a higher expression of TIMP-1 mRNA in the biopsy samples from the tumour tissue (T) than in the biopsy samples from the corresponding normal tissue (N), as determined by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). In a multivariate analysis, the T/N ratio of TIMP-1 mRNA was found to be an independent factor influencing the depth of tumour invasion and was the second most important factor in determining the prognosis of patients. As RT-PCR assay can be performed on biopsy specimens obtained before surgery, an evaluation of the TIMP-1 expression in biopsy specimens by RT-PCR may thus provide useful preoperative information on tumour aggressiveness.