The use of gold cluster focused ion beams produced by a liquid metal ion gun in a TOF-SIMS mass spectrometer is shown to dramatically enhance secondary ion emission of phospholipids and peptides. The method has been successfully tested with cells grown onto plastic slips and with mouse brain slices, without any treatment of the samples. Very reliable time-of-flight mass spectra are acquired with a low primary ion dose of a few 10(7) ions, and high lateral resolution molecular ion images are obtained for heavy ions of great biological interest. This approach offers new opportunities in pharmacological and biological research fields by localizing compounds of interest such as drugs or metabolites in tissues.