Lead isotopic ratios (206Pb/207Pb, 208Pb/207Pb and 208Pb/206Pb) and concentrations in the livers and bones of marbled teal and white-headed duck were determined in order to establish the main Pb source in these waterfowl species. Lead concentrations in bone and liver were found to be very high in many of the white-headed ducks. Some of the marbled teal had high Pb levels in the bones but liver Pb levels were all low. Ingested Pb shot were found in both species but the white-headed duck had higher prevalence of shot in their gizzards than the marbled teal. The 206Pb/207Pb ratio in livers and bones of white-headed ducks showed no significant differences compared to the ratios obtained from Pb shot. Marbled teal liver and bone Pb ratios were similar to the Pb shot ratios, with no significant differences found. Marbled teal liver and bone ratios were, however, also similar to atmospheric Pb ratios described in Spain. The 206Pb/207Pb ratio in bones of marbled teal ducklings with the highest Pb concentrations tended to resemble the ratios of Pb shot, which supports the hypothesis that the Pb was derived from the mothers. We found that the Pb ratios of Pb shot and Pb ratios described in geological formations in the area overlapped. The principal source of Pb in many of these birds was, however, most likely derived from Pb shot, supported by the similar isotopic ratios, high Pb concentrations and evidence of ingested shot. There was a larger separation for the 206Pb/207Pb liver ratio between birds with and without ingested Pb shot compared to the 208Pb/207Pb liver ratio. The 206Pb/207Pb isotopic ratio hence seems to be the most useful ratio to determine recent Pb shot ingestion.