The nature and composition of the metal-TTA complexes (M z.dbnd; Cr, Mo, W) were investigated by spectrophotometric methods applicable to a maximum concentration of 1·9 × 10 −5 M chromium, 4·16 × 10 −6 M molybdenum and 4·33 × 10 −6 M tungsten. Chromium forms CrT 3, CrT 2(OH)(H 2O), CrT 3 and CrT(SO 4) 2 2− at pH3–5·5, pH . 5·7, 1·0 M hydrochloric acida nd 0·5 M sulphuric acid respectively. Molybdenum and tungsten form MO 2T 2 type complexes (M Mo, W) at 6·0 M and 5·6 M hydrochloric acid respectively, while at 0·05 M sulphuric acid they form HMO 2T 3 type of complexes. The extraction constants of these species were calculated. The distribution ratio of TTA under various conditions was determined.