Thallium is a metal with a high rate of accumulation in the environment and at the same time there is a very large dispersion of it. Heavy metal studies and its bioaccumulation and concentration in organisms and health implications are still not well known. The aim of this study was to demonstrate the importance of this element as an intoxicant of living organisms, especially on laying hens. Four groups of ISA Brown hens were used in this study. Experimental groups received feed containing thallium as thallium sulfate (Tl₂SO₄). Concentrations and metal accumulation in the animals were determined periodically, analyzing the eggs and animal blood. After the experiment, concentrations of thallium in the tissues was determined post-mortem. The studies showed a proportional accumulation of thallium in the body of the animals in relation to exposure time, and doses with the highest concentrations in the bones, kidneys, muscles, liver, and blood.