The aim of the study was the evaluation of dermal and oral toxicity of malathion based on the results of histopathologic and ultrastructural tests. The standard of the pesticide - IPO 460 Malathion was used in the study. The preparation was suspended in oil emulsion. The study was conducted on Wistar rats. Dermal toxicity was examined in 2 groups of experimental rats. The animals were applied 8 mg (1/100 LD50) and 16 mg (1/50 LD50) of the preparation on the tail skin for 4 hours daily for a period of 28 days. In the case of oral toxicity, a dose of 1/50 LD50 malathion was used. The amount of 1 ml (11.2g) of the preparation was administered intragastrically by stomach tube for 28 days. In both experiments the control animals were administered only the emulsion used for suspending the pesticide. The following organs were subject to histopathologic and ultrastructural evaluation: liver, kidneys, heart and lungs. The histopathologic and ultrastructural changes observed showed various degrees of intensity according to the route of malathion administration and the size of the dose applied. Dermal application of the pesticide in a smaller dose did not cause histopathological changes in the organs of the animals, while the administration of a higher dose resulted in changes only in the liver. Changes on the ultrastructural level occurred in all organs and were dose-dependent. After oral administration of malathion, both histopathologic and ultrastructural changes observed in all organs were more intensified than after dermal application.