In most cases an addition of inoculants to molten cast iron is advisable and even necessary to produce good-quality castings. The mechanical properties and machinability of cast iron with nodular graphite greatly depend on the formation of graphite and the matrix microstructure and both are significantly influenced by the inoculation treatment. The mechanism of inoculation, the influence of the inoculation method and the amount of added inoculants are presented. Keywords: ductile iron, inoculation, microstructure, graphite, metallic matrix V ve~ini primerov je dodatek modifikatorjev staljenemu livnemu`elezu priporo~ljiv in celo potreben za izdelavo dobrih ulitkov. Mehanske lastnosti in obdelovalnost litega`eleza z nodularnim grafitom so mo~no odvisne od oblike grafita in od mikrostrukture osnove, na oboje pa mo~no vpliva obdelava z modifikatorji. Predstavljen je mehanizem modifikacije, vpliv metode modifikacije in vpliv koli~ine dodanega modifikatorja.