Clutches of merganser eggs were collected in 1973 and 1975 to determine whether levels of organochlorines and mercury might be responsible for possible population declines and to compare eggshell measurements with those of early museum collections. One egg per clutch was selected randomly for chemical analysis. Overall, residues of DDE, PCB?s, and mercury were low in Hooded Merganser eggs; locality means for DDE ranged from 0.07 to 13.2 ppm, PCB means ranged from 0.44 to 4.91 ppm, and mercury means ranged from 0.16 to 1.49 ppm on a wet-weight basis. Residues of DDE and PCB?s appeared to be high in Red-breasted and Common merganser eggs. DDE averaged 15.7 ppm in Red-breasted Merganser eggs and PCB?s averaged 44.6 ppm; Common Merganser eggs contained an overall mean of 19.5 ppm DDE and 61.0 ppm PCB?s. Hooded Merganser eggs from the Midwest had thinned 8.3%, but the change was not significant. Highly significant shell thinning was detected in Red-breasted and Common merganser eggs; Red-breasted Merganser eggs were 17.7% thinner and those of Common Mergansers were 23.5% thinner than museum collections.