Forty wild-type, pen-raised mallard (Anas platyrhynchos) hens were divided into 4 groups of 10. Each bird received 8, 2, 1 or 0 number four lead shot. Blood lead of treated birds exceeded normal concentrations (0.40 ppm) within 8 hours and attained maximum concentrations on the second day. Blood fluorescence spectra of these mallards, scanned on a fluorescence spectrophotometer, were characteristic of protoporphyrin IX (PP). Protoporphyrin IX is apparently synthesized and accumulated in the peripheral blood. Due to rapid leak of PP from erythrocytes and effective biliary clearance, PP concentrations were rarely elevated (>40 μg/dl) in freshly drawn blood from lead-poisoned ducks. However, when the same blood was oxygenated and refrigerated PP concentrations increased due to in vitro synthesis which terminated within two days. No such increase was manifest by controls. Blood PP exceeded normal concentrations (40 μg/dl) in blood which was drawn two days after shot ingestion and refrigerated for two days prior to testing. Maximum concentrations were attained by the eighth day. The PP concentrations had returned to normal in 90% of the lead-treated birds by the 36th day after shot administration. Sequential radiographs revealed shot clearance from the gizzards of 90% of the ducks by the 35th day. As the result of these observations a finding of a blood PP concentration above 40 μg/dl would suggest the ducks being examined ingested the equivalent of at least one lead shot approximately two days to one month prior to testing. Sixteen additional mallards (8 male, 8 female), administered various doses of lead shot, were examined daily for clinical signs of lead poisoning. Motor functions were impaired at blood PP concentrations exceeding 500 μg/dl. A commercially available fluorometer used to screen humans for lead intoxication by measurement of erythrocytic zinc protoporphyrin was modified to test ducks. This instrument is capable of measuring the PP concentration in a single drop of unprocessed blood.