The evoked potentials visual and auditory are studied in 43 patients with latent syphilis without previous mucocutaneous lesions. Twenty nine of them had not received treatment, and 14 due to their positive serology were treated with benzathine penicillin. At the visual potential evoked there were no abnormalities but in 20 cases evoked auditive potential were abnormal. This findings suppose the existence of subclinical neurological indicates the existence of lesions in almost 50% of the cases of this period of syphilis. All these patients had positive circulate immune complexes and normal cerebro-spinal fluid. The neurological alteration consists in a lesion of the cerebral trunk. According to these results the auditory potential evoked test is very important. The authors doubt on the efficacity of the benzathine penicillin in this period of syphilis.