A peptide containing the CCHH motif, the putative zinc-binding sequence of influenza virus M1 protein, was found to bind zinc in a one-to-one complex with the characteristics of a typical zinc-binding peptide. Intact influenza virus also contained zinc and we show that this zinc is bound to the M1 protein in the virus. However, only a small proportion of M1 contained zinc: 4% in virus and 6 to 9% in isolated protein. One strain, B/Yamagata/16/88, consistently contained more zinc: 15 to 20% both in virus and in isolated protein. We also determined the RNA binding and transcription inhibition activities of various M1 proteins and found that the zinc content of M1 had no influence on either activity. We suggest that the zinc in M1 has a structural role in the virion other than nucleic acid binding.