Six new 1,3-diorganylimidazolidin-2-ylidene (NHC) gold(I) complexes of the type [Au(NHC)(2)](+) (1-6), were synthesized by reacting [AuCl(PPh)(3)] with 1,3-dimesitylimidazolidin-2-ylidene or bis(1,3-dialkylimidazolidin-2-ylidene). The complexes 1-6 were fully characterized by elemental analyses and spectroscopic data. The placement of mesityl or para-substituted benzyl groups on the nitrogen atoms of the ring of the complexes leads to the particularly active antibacterial agents evaluated in this work. It is worth noting that the p-methoxybenzyl derivative (2) inhibited the growth of Pseudomona aeruginosa, Staphylococcus epidermidis, Staphylococcus aureus and Enterococcus faecalis with minimum inhibitory concentration (MIC) values of 3.12 mug ml(-1), 6.25 mug ml(-1), 3.12 mug ml(-1) and 3.12 mug ml(-1) respectively. In contrast, the analogous p-dimethylaminobenzyl derivative (3) is effective only against Escherichia coli (MIC = 3.12 mug ml(-1)). Copyright (C) 2004 John Wiley Sons, Ltd.