Phosphotriesters are often used as intermediates in the synthesis of phospholipid diesters. The use of phospholipid triesters themselves as bioactive moieties has been little studied. The masked phosphodiester approach used successfully in our group for the synthesis of nucleotides with excellent anti-HIV activity has been applied to phospholipids.Thus, phosphotriesters of diacyl glycerols (a) have been prepared and tested for their antineoplastic and antiviral activity. These triesters contain one labile group and thus act as masked phosphodiesters. A similar series of diacyl glyceryl phosphoramidates (b) has also been synthesised. Novel, structurally interesting phospholipid dimers have also been prepared and their biological activity is currently being evaluated.