In this study we investigated the tumorigenicity, growth pattern and spontaneous metastatic ability of a series of nine human colorectal carcinoma cell lines after subcutaneous and intracaecal xenografting in nude mice. CaCo2 cells were found to be poorly tumorigenic to non-tumorigenic in either site; the other cell lines were tumorigenic in both sites. SW1116, SW480 and SW620 did not show local invasive in the NCI-H716 and LS174T cells were both invasive in the caecum, but only NCI-H716 was invasive in the subcutis. HT29 and 5583 (S and E) cells were invasive in the caecum and from that site metastatic to the lungs and/or the liver. HT29 and 5583S cells were both invasive in the subcutis, but 5583E cells were not. Of each category of in vivo behaviour in the caecum, one cell line was further investigated with regard to invasion in vitro (into embryonic chick heart fragments), E-cadherin expression in vivo and in vitro and in vitro production of u-PA and t-PA. These parameters were chosen in view of their purported role in extracellular matrix degradation and intercellular adhesion, which are all involved in the invasive and metastatic cascade. Invasion in vitro was not predictive for invasion or metastasis in vivo. In the cell line which showed invasion in embryonic chick heart tissue, heterogeneous E-cadherin expression was observed in vitro together with a relatively high production of u-PA. The non-invasive cell lines showed in vitro homogeneous expression of E-cadherin with a relatively low production of u-PA. In vivo expression of E-cadherin was either absent or heterogeneous. We conclude that: (1) colorectal carcinoma xenografts show site-specific modification of in vivo invasive and metastatic behaviour; (2) invasion in vitro does not correlate with invasion and metastasis in vivo; (3) in vitro non-invasion might be associated with homogeneous E-cadherin expression and low production of u-PA; (4) E-cadherin expression in vitro differs from E-cadherin expression in vivo. The results support the notion that the microenvironment in which cancer cells grow is one of the factors involved in the regulation of invasive and metastatic behaviour.