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