Female rats were given different doses of methadone for the whole duration of pregnancy. The effects of methadone on birthweight and abstinence syndrome were studied from birth to maturation. Visual Evoked Potentials (VEP) from onset to 90 days of age were studied with averaging and frequency analysis techniques. The intensity of the withdrawal syndrome was dependent on the doses of the drug administered to the mothers, but not on the postnatal therapy (phenobarbital or methadone) administered to offspring. VEP latencies and amplitudes were not affected by fetal addiction to methadone. Thus, any long lasting alteration of spontaneous and evoked electrical activities in the visual system of fetal addicted young rats can be excluded. Only transient slight alterations of visual evoked responses are observed during the abstinence syndrome.