The effects of chronic ethanol consumption during gestation on the development of layer V pyramidal cells was studied quantitatively in the somatosensory cerebral cortex of the newborn guinea-pig. The spread of the basilar dendritic arborizations and counts of dendritic spines on the apical dendrite of neurons that had been processed with the rapid Golgi method were compared with those found in age-matched controls receiving an isocaloric diet without alcohol. There were significant differences in the number of primary basilar dendrites (P less than 0.05) and dendritic ramifications at a distance of 25 micron from the soma (P less than 0.01) between the alcohol-exposed and control animals. There also were significant differences in the number of dendritic spines on the apical dendrite (P less than 0.001). This experimental model further illustrates developmental anomalies in the cerebral cortex following prenatal ethanol exposure.