The aim of the study was the evaluation of the toxic effect of a two-component, preparation Nurelle D 550 EC (500 g of chlorpyrifos and 50 g cypermethrin per 1 l), administrated dermally. Toxicity was evaluated from histological and ultrastructural studies of the internal organs and immunotoxic effects (evaluation of phagocytical and bactericidal activity of neutrophils). The preparation for dermal application was applied in 2 concentrations (200 mg/kg/day of chlorpyrifos plus 20 mg/kg/day of cypermethrin or 1000 mg/kg/day of chlorpyrifos, plus 100 mg/kg/day of cypermethrin). The preparation was administrated on the tail skin of female Wistar rats for 4 hours daily for a period of 4 weeks. After 28 days of the experiment, the animals were anaesthetised and blood was taken from the heart to evaluate the granulocyte system. The following organs were taken for histological studies: liver, kidney, lung, heart, spleen, thymus and lymph nodes. Ultrastructural studies were carried out on the lung, liver, kidney and heart. The results of the study showed that dermal application of the pesticide Nurelle D 550 EC resulted in slight morphological and ultrastructural changes in the liver, kidney, lung and heart. The preparation examined slightly elevated the bactericidal activity of neutrophils. The differences, however, were not statistically significant. The phagocytic reaction in animals of both experimental groups did not differ from that observed in control group