A range of 14 derivatives of flavone-8-acetic acid (FAA) with a heterocyclic substituent in place of the 2-phenyl group have been prepared and their anti-tumour activity evaluated in vitro against a panel of human and murine tumour cell lines and in vivo against MAC 15A. Some of the compounds, notably 2c,d and s, showed significant in vivo activity and these require further studies in order to evaluate their potential for development.