The cluster beam technique offers promise of becoming a useful tool for chemists in their search for new compounds. Using this technique elemental vapors can be made to react under controlled conditions to form units of condensed matter (clusters) small enough to be analyzed in a mass spectrometer, but still large enough to contain several structural building blocks. Periodic patterns in cluster mass spectra often allow these building blocks to be uniquely indentified. Of particular interest is the identification of building blocks unknown in the crystalline state. The mass spectrometer has been used primarily to measure the number of atoms in elemental clusters; Xe/sub 55/, Na/sub 20/, Si/sub 10/, Ge/sub 10/ and C/sub 60/. The authors emphasize a slightly different aspect of mass spectrometry. The technique can be used to chemically analyze compound clusters.