Phosphate triester derivatives of the anti-neoplastic alkyi iyso phospholipid (ALP) have been prepared as novel potential therapeutic agents. In particular, symmetrical phosphate triesters have been prepared, using phosphorochloridate chemistry. The compounds have been fully characterised by a range of techniques, and assayed for their inhibition of DNA synthesis by mammalian cells in culture. The compounds are generally inhibitory towards DNA synthesis in the pM range. However, the magnitude of the effect varies greatly with the phosphate structure; alkynyl and glycol substituted phosphates being especially potent.In a recent paper [13] we described our initial results regarding the synthesis of some novel ALPs, modified in the phosphate region. It was a notable and surprising observation that simple dialkyl blocked phosphate derivatives are active in vitro and that simple structure activity trends appear to operate. In this paper we describe the synthesis of some novel ALPs, further modified in the phosphate region in the hope of improving activity at lower concentration, and we discuss their evaluation in vitro. In particular we study the effect on anti-cancer activity of substitution within the alkyl-phosphate region.