The aim of the present study is to evaluate the seasonal fluctuation of heavy metals in the isopod Porcellio laevis at four uncontaminated subtropical locations. This study was carried out at four different field sites in Assiut, Egypt. The concentrations of cadmium, lead, copper, and zinc in animal, soil, and litter (mug/g dry weight) were monthly recorded during the period from June 2002 till May 2003. There was little difference in metal accumulation trends between the sites. In general, the isopod showed significant increased Pb and Zn concentration during summer and spring months, whereas this was not the case for Cd and Cu. The bioaccumulation (BAF) and bioconcentration factors (BCF) of the metals revealed marked seasonal changes throughout the year. Generally, BAF of metals were higher during summer and spring, and BCF were higher during summer and autumn. Comparing the metal accumulation with climatic fluctuations (measured) it was speculated that temperature was the main factor causing seasonal fluctuations of the internal metal concentration in the isopod.