Cells in tumors may be exposed to adverse conditions such as nutrient deprivation, acidic pH and hypoxia. It has been shown previously that exposure to hypoxia, acidosis and glucose starvation in vitro increases the experimental metastatic ability of murine KHT-LP1 sarcoma, SCC-VII squamous carcinoma and B16 melanoma cells. This effect was most marked when cells were allowed to recover under normal in vitro growth conditions before injection. In the present study we examined whether the invasive capacity of the cells could be influenced by these modifications of the cell microenvironment. We used Matrigel, a basement membrane-like preparation in a two-chamber invasion assay to address this issue. Both KHT-LP1 and SCC-VII murine cell lines showed an increased ability to invade through Matrigel after hypoxia, and glucose starvation, but there was no consistent change in invasive capacity following acidosis exposure. The results for hypoxia and glucose starvation are in agreement with our previous studies of metastatic ability for these cell lines and we confirmed this for KHT-LP1 cells exposed to hypoxia in the current study. In parallel with the invasion assays, we compared cathepsin (L + B) content of the cells in treated and control suspensions. The effect observed varied according to the cell line and the treatment received (hypoxia, glucose starvation). There was an increase of cathepsin content for KHT-LP1 cells exposed to hypoxia and this increase correlated well with the increase of the invasion ability through Matrigel. We did not observe any increase of cathepsin for hypoxia-treated SCC-VII or for KHT-LP1 and SCC-VII cells treated with glucose starvation. These results suggest that transient hypoxia and glucose starvation can increase the invasive ability of tumor cell lines and thus may cause tumor progression by facilitating the invasive step of the metastatic process. The increased levels of cathepsin (L + B) in the KHT-LP1 cells treated with hypoxia, compared to control non-treated cells, may play a part in this increased invasive capacity.