In oral squamous cell carcinomas, focal or extensive loss of basement membrane components and of integrins has been reported. The purpose of this study was to investigate whether those regions of the tumour-connective tissue interface which lack laminin and type IV collagen coincide with areas of loss of the alpha 6 and beta 4 integrin subunits on basal keratinocytes. Out of a total of 15 poor and moderately or well differentiated squamous cell carcinomas, all showed some loss or fragmentation of basement membrane proteins and in 12 the loss was coincident with loss of alpha 6 and/or beta 4. In three cases, there was loss of basal integrin expression in areas where the basement membrane remained intact. These results provide further evidence that loss of integrins may play an important role in tumour progression and prompt us to speculate about the sequence of events leading to tumour invasion.