Residues of organochlorine chemicals (OC) including polychlorinated biphenyls (PCB) were analyzed by gas chromatography in carcasses of young arctic terns (Sterna paradisaea) and common terns (Sterna hirundo). The birds found dead were collected in 1988 in a breeding colony of the German Wadden Sea. The birds were separated into two age-groups (2–14 days old and 15–27 days old). Most of the chemicals showed a higher concentration in younger birds. In contrast, the absolute amount of the chemicals was greater or at least equal in older birds. If food contamination is as high as shown in this study, the accumulation of chemical hazards in growing terns can only be recognized by measurement of the absolute content, because the concentration is diluted by growth effects. In comparison to food samples from the same breeding colony, one can recognize an accumulation from one trophic level to the next. This study proves that prefledging terns can be accepted as bioindicators. Presumably the residues of OC alone did not cause the death of the terns, yet they were definitely important stress factors.