Being a sediment feeder, the lugworm Arenicola marina could be a suitable candidate organism for the biomonitoring of sediment-bound contaminants in intertidal areas. Since lugworms are only rarely used in environmental monitoring, little is known about the natural variation in their body residue levels. In this study, we assessed the importance of seasonal fluctuations, spatial variation and sexual development to polycyclic aromatic hydrocarbon (PAH) residues in lugworms. Over a period of 15 mouths, lugworms were sampled along a contamination gradient in the Western Scheldt estuary in the Netherlands. A clear seasonal pattern in the body residue levels of PAH was observed, with lowest levels in March and highest levels just prior to the spawning season in September. During the spawning season the body residue levels showed a marked decrease. Although this seasonal pattern is apparently related to the reproductive cycle of the lugworm, no clear differences in body residue levels were found between animals with or without developed gonads. The contamination gradient, present in the estuary, was clearly reflected in the body residue levels of PAH. The expected gradient of internal concentrations was, however, absent in October, when the spawning period was not yet finished. The variation in lugworm body residue levels was smaller than the fluctuations in sediment PAH levels. It can be concluded that the lugworm is a suitable organism for the biomonitoring of sediment-bound contaminants, provided that attention is paid to its reproductive cycle.