An organic extract of Nitzschia alba cells possesses ionophoretic activity towards silicate, as it induces silicate transport across an organic phase or across synthetic lipid membranes. The activity is dependent upon Na+ and prefers silicon to germanium, a congener. The activity can be resolved into two apparently pure fractions by a combination of high performance liquid chromatography and thin-layer chromatography. Preliminary characterization indicates that the compound(s) contains vicinal hydroxyl groups but is devoid of amino, sugar or phosphate groups.