Laboratory experiments were undertaken to study uptake and retention of antimony and to investigate whether the elevated organ antimony concentrations found previously in a population of Microtus agrestis at a contaminated site could cause harmful effects. Antimony trioxide in the diet produced elevated organ concentrations, but even in a 60-day experiment no harmful effects were evident. An equilibrium between uptake and excretion of antimony seemed to be rapidly established and progressive increases in organ concentrations did not occur. When dietary intake was terminated antimony was rapidly cleared. Comparison of findings from the laboratory and field suggested that inhalation was an additional route of intake in the field. It seems that present levels of antimony are unlikely to cause toxic effects in the wild population.