The invention features an improved lipid formulation comprising a cationic lipid of formula (A), a neutral lipid, a sterol and a PEG or PEG-modified lipid, where R1 and R2 are independently alkyl, alkenyl or alkynyl, each can be optionally substituted, and R3 and R4 are independently lower alkyl or R3 and R4 can be taken together to form an optionally substituted heterocyclic ring. In one embodiment, R1 and R2 are independently selected from oleoyl, pamitoyl, steroyl, linoleyl and R3 and R4 are methyl. Also disclosed are targeting lipids, and specific lipid formulations comprising such targeting lipids.
