Retinal neurons are generated in overlapping growth spurts with ganglion cell and cone populations peaking sooner than rod and bipolar cell numbers. As such the functional development of the inner and outer retinal components and elements within these strata (rods vs. cones) may differ. We considered the postnatal development of the postreceptoral components of the ERG (P2, oscillatory potentials) in the guinea pig. ERGs were also evaluated across albino and pigmented strains in order to consider the role that pigmentation has for functional development. Electroretinograms were collected on postnatal days PD1 to PD60 (n = 4–7 per time point). The postreceptoral P2 amplitude and implicit time was extracted (digital subtraction of modelled P3 and filtering, 0.5–49 Hz). Intensity–response relationships were described using Naka–Rushton functions whose parameters were compared using a nonparametric bootstrap. Oscillatory potentials (OPs) were extracted following signal conditioning and filtering to remove the a- and b-waves and were described using a Gabor function. OP response parameters were compared using repeated measures ANOVA. Postreceptoral P2 amplitudes mature soon after birth (PD10–PD12). Oscillatory potentials show a similar postnatal amplitude development (PD10–PD12) but a later maturation in timing (PD20) compared with the postreceptoral waveform. All components (P3, P2, and OPs) declined at the same relative rate with age after PD12. Albino animals gave larger, faster, and more sensitive waveforms at all ages but showed the same age-related trends as did pigmented animals. Early development of inner retinal synapses in guinea pigs may underlie the rapid postnatal maturation of their postreceptoral response. These appear to be constrained by the development of receptoral responses. All components declined at the same rate suggesting either a change in the photoreceptoral response or changes to ocular impedance with age.