The nm23 gene production has been heralded as a suppressor of metastasis in many human tumours but it is not clear at which stage in the metastatic process nm23 protein exerts its effect. The aim of this study was to test whether nm23 protein is associated with occurrence or category of angioinvasion. We have made use of the well documented fact that follicular carcinoma of the thyroid may show vascular invasion whereas papillary carcinomas may metastasis via the lymphatics. 65 thyroid tumours (20 follicular adenomas, 22 papillary carcinomas, 23 follicular carcinomas) were stained for nm23 protein using an immunopurified polyclonal antibody. Nm23 protein status showed no correlation with category of thyroid tumour. This is indirect evidence that nm23 does not suppress metastasis by influencing vascular invasion in this tumour type.