To assess the bioindicator value of parasites, the concentrations of six heavy metals (Cr, Cu, Pb, Cd, Ni and Zn) were analyzed by atomic absorption spectrometry in gravid females of the nematode Philometra ovata, body cavity parasites of gudgeon (Gobio gobio) and muscle samples of infected and uninfected hosts. The concentration of heavy metals was significantly higher in specimens of P. ovata compared to the host muscle tissue. The parasite-to-muscle ratio of heavy metals varied from 3.2 to 121.7, in increasing concentrations for Cr, Cd, Cu, Pb, Ni and Zn. The presence of parasites did not influence the heavy metal content of the hosts, and no significant differences were found between muscle tissues of parasitized and non-parasitized fishes. The bioconcentration factor (BF = Cparasite/Csediment)varied between 0.4 and 25.8, in increasing order for Cd, Zn, Cu, Pb, Ni and Cr. These results indicate that P. ovata may serve as sensitive indicator species of heavy metal pollution in freshwater ecosystems.