The experiments were performed on 262 laying hens divided into 8 groups: 5 groups of hens were given orally N-nitrosodimethylamine (NDMA) in single doses of 30, 10, 3, 1 and 0.1 mg/kg of body weight, two groups received tap water containing 2 and 5 mg NDMA/kg, provided ad libitum for 20 consecutive days, and one group of layers served as a control. Birds were selected at random and sacrificed at one or two day intervals and NDMA content was determined in blood, muscles, liver, brain and in collected eggs. The highest concentrations of NDMA were found 24-36 hours after dosing in all investigated tissues and eggs. A single oral dose of 0.1 mg NDMA/kg produced tissue levels up to 0.06 mg/kg and resulted in excretion of detectable amounts of the carcinogen in eggs for up to 6 days. After large doses, 10 mg and 30 mg NDMA/kg, concentrations in corresponding tissues reached 6.0 and 12.7 mg/kg, and the presence of NDMA in eggs could still be detected after 12 and 14 days. Birds receiving NDMA in drinking water showed increasing NDMA concentrations in all analysed tissue and eggs. After 12 days, the highest levels were found in eggs, blood and brain. Practical implications of the results must be evaluated from the point of view of human safety.