This investigation has focused on whether a number of molecular species, which have recently been recognised as components of cell attachment receptors utilised in recirculatory leukocyte traffic, are expressed on metastatic tumour cell populations. This has been studied on live cultured metastatic and non-metastatic tumour cell lines as well as on histological sections of frozen tissue from primary tumours and metastases which they formed after inoculation into nude mice. Here we report data we have obtained using immunofluorescence microscopy, fluorescence activated cell analysis, immunocytochemistry and pathological investigation of tumour behaviour in vivo, which converge to indicate that expression of the integrin molecule VLA-4 is positively associated with the execution of the metastatic process. This molecule is known to be a receptor for at least two ligands, namely the inducible endothelial adhesion molecule VCAM-1 and the extracellular matrix component fibronectin, and is thought to be mechanistically important in the attachment and diapodesis of lymphocytes. The present findings, indicating differential expression of this molecule on metastatic cell populations relative to non-metastatic cell populations, support and extend recent reports from other laboratories, of the presence of various leukocyte adhesion receptors on metastatic tumour cells. This accumulating evidence suggests that inappropriate expression of one or more of these surface adhesion molecules in tumour cell lineages may endow the progeny of the affected clones with some of the properties needed for metastatic behaviour. The total information so far assembled by various groups also provides some early clues suggesting that the types of molecules expressed may be related to the histogenetic origin of the tumour and its pattern of metastatic spread.(ABSTRACT TRUNCATED AT 250 WORDS)