The somatic lipids (from root, stem, or leaves) of one species from each of the genera : Ximenia (Olacaceae), Santalum and Leptomeria (Santalaceae) have been examined and the presence of the following acids established : (i) octadeca-trans-13-ene-9,ll-diynoic acid, (ii) octadeca-trans-11,trans-13-dien-9-ynoic acid, (iii) octadeca-trans- 11-en-9-ynoic (ximenynic) acid, and (iv) an octadeca-trans-trans-dienediynoic acid, not yet fully identified. The occurrence of (ii) and (iv) in Nature has not been previously observed. The seed fat of Leptomeria aphylla R.Br. has been examined and found to contain some 20 per cent. of ximenynic acid as glycerides. No conjugated polyunsaturated acids were found in the lipids of the sole Australian representative of the closely related Belanophoraceae family.