To study the harmful effects of organic concentrates from tap water on mammal animals in vivo.Organic pollutants were absorbed with resin XAD-2 from tap water and administered the mice via a stomach tube or intraperitoneal injection. Micronucleus rate in bone marrow polychromatic erythrocytes, testicular chromosome aberration rate, indices for immune functions and the activity of ethoxyresourufin o-deethylase (EROD) in S(9) fraction of the liver were determined.Micronucleus rate and chromosome aberration rate increased by 1.7 and 3.5 folds, respectively, after administration of high dose of organic pollutants from the tap water (200 liters of tap water per kilograms of body weight) for three days. Humoral immunity and non-specific immune functions were obviously inhibited after administration of low-dose (6 L/kg). In addition, organic concentrates from tap water also could significantly induce the activity of EROD, with a good dose-dependent relationship.Organic concentrates from tap water could cause chromosome damage to somatic and germ cells and decrease in immune functions in the mice, as well as they could induce the activity of cytochrome P448 in the liver microsome. It suggested that organic pollutants concentrated from tap water had potential carcinogenic effects on mammal animals.