The feasibility of using dysprosium as an inert marker for digestibility studies with swine has been investigated. Eight barrows and eight gilts of initial weight averaging 65 kg were fed four different diets with crude fibre levels ranging from 4.1 to 10.2%. Dysprosium was included in the diets at 25 ppm and the induced radioactivity in feed and fecal samples, following irradiation in the Canadian SLOWPOKE reactor, was measured with a Ge(Li) detector coupled to a 4096 multichannel analyzer. Dysprosium was evenly distributed in feed and fecal samples. Ingested dysprosium was quantitatively recovered in feces and there was no evidence of variation in its daily excretion following a 7-day adaptation period. Dry matter and crude protein digestibility coefficients obtained with the dysprosium ratio technique were not significantly different from those determined by means of total fecal collection. The present results indicate that dysprosium, as determined by instrumental neutron activation analysis, can be used as a reliable indicator in swine digestibility studies.