A large number of substituted ethylenediamine complexes of platinum (II) and platinum(IV) have been prepared and characterised, and their anti-tumour activity tested against sarcoma 180, leukemia L1210, and ADJ/PC6A plasma cell tumours. In general these complexes are less active than simpler amine analogues, though several complexes show activity against all of the screens. Difference in activity of platinum(II) and platinum(IV) analogues leads us to cast doubt on the "in vivo reduction" theory hitherto used to describe the action of platinum(IV) complexes.