Lipases were shown to catalyze acylation of various sulfonamides using water or ionic liquids (ILs) as solvents. Ionic liquids that were used include [bmim] [PF6], [bmim] [N(Tf)(2)], and [bmim] [BF4] (where bmim = 1-butyl-3-methylimidazolium, PF6 = hexafluorophosphate, N(Tf)(2) = bis(trifluoromethylsulfonyl)imide, and BF4 = tetrafluoroborate). As a function of the lipase nature the ionic liquid can be or not a suitable solvent for this reaction. Therefore, it may be stated that an optimization of the process implies a molar ratio of 1:3, the use of lipase PS Amano as catalyst and the use of [bmim][N(Tf)(2)] ionic liquid as solvent. A comparison of the systems shows that the reactivity of the enzyme in [bmim] [N(Tf)(2)] ionic liquid was generally lower than in water but the selectivity to monoacylated sulfonamide was always 100%. (c) 2007 Elsevier B.V. All rights reserved.