The influence of minerals belonging to six classes of silicates on the induction of interferon (IFN) by influenza-virus was tested in Rhesus-monkey kidney cell monolayers. Silicates were ground to particles of about 1 micron diameter and sterilized as stock solutions. IFN was assayed by viral inhibition, and influenza-virus multiplication was measured in silicate exposed cultures. Inhibition of IFN induction by nenosilicates, cyclosilicates, and inosilicates was either insignificant or 50 percent or greater. Among inosilicates, wollastonite (13983170), pectolite (13816472), and rhodonite (60997195) increased the production of IFN by two to three times. Inhibition of IFN induction was demonstrated by all the phyllosilicates and tectosilicates tested. Coating the minerals with poly(4-vinylpyridine-N-oxide) reduced the inhibitory effect of silicates on the induction of IFN. All nine randomly selected silicates, which inhibited the induction of viral IFN, failed to affect the antiviral cellular resistance induced by IFN added exogenously to cell cultures. Pretreatment of monolayer Rhesus- monkey kidney cells with silicates resulted in increased multiplication of influenza virus and reduced concentrations of IFN. The authors conclude that natural silicates have a variety of effects on the induction of viral IFN, ranging from inhibition to stimulation, indicating that some of them may increase susceptibility to viral infection by affecting the viral IFN induction process.