The accumulation of cadmium in Moniliformis moniliformis parasitizing experimentally infected rats that had been orally exposed to cadmium was investigated in this study. Cadmium accumulation in the helminth and in different tissues of the host was determined using electrothermal atomic absorption spectrometry (AAS) after a 3-week period of exposure. The mean cadmium concentration measured in M. moniliformis was 5.8 μg g−1 wet weight, which was 20, 23, and 119 times higher than that determined in the kidney, liver, and intestine of the host, respectively. Although female worms accumulated higher amounts of cadmium than did males, no tendency emerged between the cadmium concentration and the weight of individual acanthocephalans. This study reveals that cadmium accumulation also occurs in archiacanthocephalans, but to a lesser degree than in palaeacanthocephalans parasitizing fish. Due to its cadmium-accumulation capacity, M. moniliformis might be used as a highly sensitive free-living bioindicator in terrestrial and urban ecosystems.