The lipase gene family comprises three vertebrate genes, lipoprotein lipase (LPL), hepatic lipase (HL) and pancreatic lipase (PL), that are derived from a common ancestral gene. While these lipases are functionally related, considerable evidence indicates that LPL and HL share a higher degree of structural homology than either shares with PL (1 –4 ). For example, it has been established by a number of different methods that LPL and HL are functionally active as homodimers, while PL is active as a monomer (5 –9 ). However, there are discrepancies reported in the literature, namely the findings of monomeric functional units of LPL and HL by Ikeda et al. (10 ) and Schoonderwoerd et al. (11 ), the latter concluding that the functional unit of rat HL in the liver is a monomer, while in adrenal gland and ovary it might be a dimer.