Characterization of (benzoyloxymethyl-NNO-azoxy)methane, from benzoylation of the cycasin aglycone methylazoxymethanol, commonly referred to as MAM, is reported. Crystal structure analysis shows that the azoxy substituents have the Z configuration. Crystals are monoclinic, space group P21/c, a 7·436(2), b 8·771(2), c 14·640(1) Å, β 90·73(1)°, Z 4; the structure was refined to final R 0·048 by using 1171 reflections with I ≥ 3·0σ(I ). Subcutaneous injection of (Z)-(benzoyloxymethyl-NNO-azoxy)methane in mice showed liver changes typical of the corresponding MAM acetate-induced hepatotoxicity. This permits correlation of hepatotoxic effects with the Z configuration of the aglycone. Histological examination of the brain and spinal cord revealed no significant changes at a dosage of 52· 6 mg/kg.