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The objective of the investigation was to evaluate quantitatively the analgesic efficacy of the Ketamine-Azaperone-general anesthesia during surgical procedures on pigs by nociceptive flexor reflexes (NFR). The study was performed in 30 four to five month old male pigs which were castrated. The NFR was evoked every minute over the N. ulnaris by multiple electrical stimulation consisting of five single stimuli (2 Hz). The reflex response was derived electromyographically (EMG) by surface electrodes placed over the M. deltoideus. The root-mean-square amplitude within the time interval of 80-240 ms after the last stimulus was calculated as measure for the reflex size. The threshold was fixed at 40 microV. Beside electrical NFR recording the surgical tolerance was determined by the traditional interdigital reflex and the defense reaction to defined surgical test stimuli which were incisisions in the scrotal skin, in the tunica vaginalis and in the testis, pulling off the spermatic cord, clamping and cutting off the spermatic cord and final wound disinfection. All surgical pain stimuli were performed simultaneously with the electrical stimuli. After induction of anesthesia the NFR amplitude declined from 3500 microV below the threshold of 40 microV. At 98% of the surgical stimuli without defense reaction were below the reflex threshold. At 93% with defense reactions demonstrated reflex amplitudes above the threshold. When the interdigital reflex was suppressed, 89% of the NFR values fell below the threshold of 40 microV. These findings demonstrate a good correlation of NFR-amplitudes with reactions to traditional controls of analgesia.