The physiological development of the retina was followed by recording ERGs and OPs from kittens of different ages. We found that different properties of the retina attain adult values at different ages: the b-wave elicited by higher stimulus intensities became adultlike by five to seven weeks while the b-waves elicited by lower stimulus intensities required another 3-5 weeks; the implicit time for the b-waves elicited by the full intensity stimulus attained adult values by 10 weeks of age; and the oscillatory potentials did not become adultlike until 18 weeks of age. The physiological development of the ERG was related to the development of the photoreceptors and the ganglion cells as well as to the morphological development of the second order neurons. It was concluded that the physiological development, as the morphological development, proceeds in three stages: an initial slow phase during which the late receptor potential and the b-waves are first recorded; a second rapid phase, during which the amplitude of the b-waves and OPs increase rapidly; and a third slow differentiation phase during which the final development of the properties of the retina are attained.