Although birds have been frequently used as indicators of heavy metal pollution, few studies have examined pollutant levels in nestling passerines. In this paper we determined the levels of two essential (zinc and copper) and three nonessential heavy metals (lead, cadmium, and arsenic) in the excrement and feathers of great (Parus major) and blue tit (Parus caeruleus) nestlings at a polluted site (near a metallurgic factory) and a reference site (4 km farther east). The excrement of both great and blue tit nestlings contained significantly higher concentrations of arsenic, cadmium, copper, and lead at the polluted site. Zinc concentrations did not differ significantly between sites for both species. The feathers of great and blue tit nestlings accumulated significantly higher concentrations of lead at the polluted site than at the reference site. Zinc levels in the feathers of great tit nestlings were significantly higher at the reference site than at the polluted site. For all other elements considered, concentrations did not differ significantly between the two sites. There were no interspecific differences in metal levels between great and blue tits in both excrement and feathers. There was a significant positive correlation between the lead concentration in the excrement and feathers for both great and blue tits. We therefore conclude that excrement of great and blue tit nestlings can be used as a biomonitor for heavy metals (lead, cadmium, arsenic, and copper), whereas feathers appear only to be suitable as a biomonitor for lead pollution.