The reported investigations were carried out on female Wistar rats which were given at 72-hour interval during 117 days (40 doses) dichlorphos subcutaneously, intragastrically and percutaneously, and chlorphenvinphos, bromphenvinphos, methylbromphenvinphos and phospholine subcutaneously in doses amounting to 5% of LD50. After the 40th dose the animals were weighed and killed, blood and organs were taken for investigations. The activity of AChE was determined in the erythrocytes, brain, tibialis muscle and liver. In the serum the levels of transaminases (AspAT, AlAT), alkaline phosphatase, cholesterol and phospholipids were determined. Histomorphological and histochemical investigations included the liver, kidneys, myocardium, femoral muscle, diaphragm, hypothalamus, gastric wall and abdominal sympathetic ganglia. A statistically significant fall of body weight was observed in all intoxicated animals as compared with controls. The mean AChE activity was about 50% of the activity in the control group. A decrease was found also in the cholesterol-phospholipid ratio in the intoxicated animals. Degenerative changes in the parenchymal organs developed independently on the route of poison administration and they included particularly the liver (atrophy of parenchyma) and myocardium (hyperaemia, extravasations, early necrotic changes of muscle fibres, nuclear pyknosis). Necrosis and oedema were observed also in the neurons of sympathetic ganglia. The greatest intensity of the lesions was found after intoxication with the agents which were most potent AChE inhibitors (phospholine and chlorphenvinphos).