Organophosphorus compounds (OPC) are widely used as insecticides and cause a high number of acute and chronic intoxications in man. Their toxicological properties lead among others to disturbances of the central nervous system. Hearing disturbances have been reported after chronic exposure to OPC, and changes in bioelectric brain activity have been observed during the acute state of intoxication. The EEG showed no characteristic alterations. We performed a threshold auditory brainstem response (ABR) in 12 mini pigs before, during and after paraoxon (a typical OPC) intoxication with a high dose of 27 mg/kg BW. During the application of paraoxon we saw a prolongation of the interpeak latencies Jewett I-V of approximately 1 ms. A threshold shift of 10-20 dB was seen in 8 animals. After the application, while the systemic effect of the paraoxon intoxication was still apparent, the threshold shift disappeared except for 2 animals and the prolongation of the interpeak latencies could not be observed any more. No characteristic signs of paraoxon intoxication could be seen in the ABR after the application was completed. Acute intoxication with an OPC only leads to temporary, limited hearing impairment and increased interpeak latency. We could not observe characteristic changes in the ABR corresponding to the state of intoxication.