Adult mallard drakes were exposed for approximately 14 weeks to distributions of 17.8, 89.0, and 178 g of particulate lead per m² in simulted-marsh areas. The ante-mortem and post-mortem findings indicated that exposures of 17.8 g of particulate lead per m² had a low toxicity for the experimental birds. The birds exposed to 89.0 g/m² experienced a 57% mortality within an average of 72.5 days; all had positive fluorescent erythrocyte tests; and post-mortem examinations showed evidence of chronic lead toxicosis. The birds exposed to 178 g/m² showed overt signs of lead poisoning; they experienced 100% mortality within an average of 22.5 days; and post-mortem examinations showed evidence of subacute lead toxicosis. It was concluded that distributions of disintegrated lead shot (i.e. particulate lead) in waterfowl wetlands could probably exceed existing distributions of commercial lead shot in heavily hunted areas by ten fold without presenting a significant toxicity to waterfowl.