Forty-one eggs of merlin (Falco columbarius) collected in Norway between 1978 and 1994 were analyzed for persistent environmental pollutants. The mean levels of p,p'-DDE and PCBs were 9.4 (range 1.8–39.9) μg/g and 1.5 (range 0.25– 6.6) μg/g fresh weight, respectively. HCB, HCHs, dieldrin and chlordanes all had mean levels of approximately 0.1 μg/g, mercury 0.25 μg/g, whereas mirex only had 0.005 μg/g. Migration counts indicated that the Fennoscandian merlin population declined from the 1950's through the early 1960's, with a subsequent recovery from the 1970's to the 1990's. Comparisons with eggs from museums showed that the shell thinning in all decades after 1947 was more than 10%, exceeding 15% in the 1960's and 1970's. Persistent pollutants, especially DDE, probably affected population size. Eggshell thickness was significantly and negatively correlated with the DDE concentration in the egg. Pesticide levels were generally decreasing during the period covered by the study, and a parallel improvement in shell thickness was observed. Ringing recoveries indicated that different wintering areas were used by merlins from northern and southern Norway. This was a possible contributing factor for the observed regional variation in pollutant concentrations.