Both slow waves and bursts of spike potentials were recorded prior to birth in dogs and sheep. At 0l7-0.8 of term the slow-wave frequency of the jejunum did not exceed 12/min. It increased in a similar way during the last stage of fetal life in sheep and after birth in dogs. Adult values were attained 10-15 days after birth in the lamb but only by 40 days of age in the puppy. In both species, three stages of development of the spiking activity were identified. Stage 1, termed unorganized spiking activity, was converted in the fetal lamb at 0.8 of term to a fetal pattern (stage 2) characterized by cyclic 3- to 4-min periods of regular spiking occurring at 10- to 20-min intervals and propagated along a short intestinal segment. Stage 3, which corresponds to myoelectric complexes, occurred during the last 10 days of fetal life. In dogs, the fetal pattern (stage 2) was recorded from 5 days before to 15 days after birth. Stage 3 was seen in the 15-day-old neonate. The results suggest that the patterns of electrical activity seen in the last third of fetal life can be related to their function of mixing and absorbing but not expelling intestinal contents. They indicate that the electrical phenomena of the gastrointestinal tract are in accord with the overall greater maturity and independence of the newborn sheep compared to the dog.