In contrast to wild-type vesicular stomatitis virus (VSV) of Indiana (Ind.) origin which express interferon (IFN) inducing- and IFN induction-suppressing activities as mutually exclusive properties, individual particles of wild-type VSV of the New Jersey (N.J.) serotype (Hazelhurst [H] isolate) paradoxically can both induce IFN and suppress its induction in cells coinfected with a potent inducer of IFN. The properties of IFN induction, and its suppression, appear to reside in the particle that manifests infectivity. Analyses of IFN induction dose-response curves to measure IFN-inducing particles (IFP), and IFN yield-reduction curves to measure IFN induction-suppressing particles (ISP) generated by VSV-N.J.(H) in aged chick embryo cells revealed that (i) a single particle per cell sufficed to induce a quantum (full) yield of IFN, or to suppress fully IFN production by a coinfecting inducing virus, and (ii) the addition of one or more IFP per cell did not suppress the yield of IFN beyond the plateau level. The time-course of IFN production in chick cells infected with VSV-N.J. (H) revealed about a 4-h lag, even when the cells were coinfected with a potent inducer that normally induced IFN 1 or 2 h sooner. Thus, VSV-N.J.(H) appears to regulate the production of IFN in cells--even that initiated by other inducers. Expression of IFP and ISP activities both required primary transcription, with respective genomic targets similar to those reported for VSV-Ind. N.J.(H) is the first wild-type VSV observed to express IFP and ISP activities concomitantly. A model is presented to suggest how these two antagonistic properties might be expressed by a single infectious particle.