The Delta5-desaturase from Bacillus subtilis has been cloned in Escherichia coli BL21 cells and its enzyme activity has been investigated as a function of temperature and oxygenation by analyzing methyl ester adducts from the total lipid extract in GC-MS measurements. The present data bring out that the activity of recombinant Delta5-desaturase, at 20-22 degrees C and 20% oxygen, is surprisingly high yielding 22% of C16:1,Delta5 (5-cis-palmitoleic acid) and 13% C18:2, Delta5 Delta11 (efedrenic acid). Lower amounts of other mono- and doubly-Delta5-unsaturated fatty acids were also detected. These findings demonstrate that Delta5-desaturase can accept a multiplicity of substrates and is endowed with an unprecedented activity among other acyl-lipid desaturases thus representing a unique tool for the production of rare Delta5 unsaturated fatty acid derivatives.