Enzyme catalyzed isomerisation of 1,2-dipalmitin into the 1,3-isomer is shown to occur with 1,3 regiospecific lipases. The mechanism of this transformation is elucidated and the crucial role of the water still present in the enzyme preparation is shown. Thus, the first step is the hydrolysis of the dipalmitin followed by the isomerisation of the 2-monopalmitin into the 1-monoester. The last is then esterified into the 1,3-dipalmitin.