The zinc finger transcription factor 'SNAIL' was first identified in Drosophila and, along with 'twist', a basic helix-loop-helix transcription factor, is indispensable for mesoderm formation. SNAIL is a repressor of mouse E-cadherin transcription, with expression of SNAIL inversely correlated with expression of E-cadherin. Abnormal expression of SNAIL could underlie the tumorigenic conversion of epithelia associated with loss of E-cadherin expression through screening mouse and human cell lines and by in situ hybridization of primary human tumors undergoing malignant progression.