The aim of study was evaluation of the concentration of dermally applied ¹⁴C DDT in the organs of rats, and evaluation of histological and ultrastructural changes after the dermal application of unlabelled DDT standard in the organs of rats, in which the presence of this pesticide was determined by the radio-isotopic method. ¹⁴C DDT of radiochemical purity of 97% was applied in the study. The activity of the preparation per 1 cm² of the tail skin was 22.2 KBq-(175.38 microg DDT). The material for the study was taken directly after single exposure and 6 h, 8 h, 10 h, 12 h, 14 h, 18 h and 20 h after exposure. The following organs were taken for the determination of radioactivity of tissues: brain, heart, lung, liver, kidney, skin at the site of exposure. Unlabelled chemically pure, DDT (99.7%) was used to evaluate histological and ultrastructural changes after dermal application. Experimental animals received an oil emulsion of DDT (10 mg/9 cm²), applied to the skin of the tail for 4 weeks. The time of exposure was 4h daily. The animals of the control group were dermally exposed to the emulsion at the same time and under the same conditions. 4 h after dermal exposure it was observed that the preparation applied on the surface of 9 cm² in the amount of 1.578 microg was present in the skin in the amount of 1 microg/9 cm² (0.11 microg/cm²), i.e. 0.063% of ¹⁴C DDT applied dose. Directly after dermal application lasting 4 h the greatest amount of ¹⁴C DDT was noted in the liver-0.285 microg, i.e. 0.033 micrcog/g. Histopatological and ultrastructural changes were observed in the liver, kidney, lungs and heart.