Reduced expression of the tissue transglutaminase in both murine and human tumours has been consistently associated with tumour growth and progression. To investigate the functional effects of transglutaminase expression we have transfected a constitutive human tissue transglutaminase expression construct into a highly malignant hamster fibrosarcoma cell line Met B. Met B clones expressing the exogenous tissue transglutaminase exhibited a reduced incidence of primary tumour formation and an increased adherence to tissue culture plastic and fibronectin coated surfaces when compared to transfected and non transfected control cells. Transglutaminase transfected clones exhibited no significant differences in their growth rates measured in vitro, cell morphology or levels of spontaneous apoptosis measured by the determination of detergent insoluble apoptotic envelopes. The data demonstrates a suppressive effect of tissue transglutaminase on tumour growth and confirms its importance in the phenotypic changes associated with the cancer process.