The use of ion probes for microscopy and imaging microanalysis by secondary ion mass spectrometry (SIMS) is a destructive observational technique that can provide information inaccessible to the electron microscope. The damage to the sample caused by the ion-induced sputter erosion of its surface layers is exploited to identify and map the chemical and isotopic composition of the removed layers. Particularly good image resolution (20-70 nm) can be attained with heavy-ion focused probes, as with the University of Chicago 40 keV Ga+ Scanning Ion Microprobe (UC SIM). The application of this instrument to biological research involving mineralized and soft tissue has been evaluated on several occasions, together with the requirements of specimen preparation for SIMS analysis. In a review recently presented, studies of mineralized tissues (bone, teeth) were discussed. We concentrate here on recent directions of our SIMS studies of soft biological material.The sensitivity of SIMS to isotopes of any mass paves the way for the profitable use of tagged, tracer molecules in a host of biological applications as a preferable alternative to the use of radioisotopes and autoradiography.