The time course of natural cell death was studied postnatally in the ganglion cell and inner plexiform layers of the retina in the developing mouse. We examined congenic wild-type, albino and pearl mutants from birth to 12 days of age. In both wild-type and albino mice, natural cell death proceeded with an increasing rate from birth to a peak 6 days after birth, and with a decreasing rate thereafter. In contrast, cell death in pearl mutants proceeded with essentially a decreasing rate postnatally. The populations of neurones and glial cells in the ganglion cell and inner plexiform layers of the retina were also determined in adult mice. It was shown that pearl mutants had a slightly smaller number of cells in those layers than both wildtype and albino mice, and that the difference was probably due entirely to the numbers of neurones. We conclude that the pearl mutation in the mouse affects the timing of developmental cell death, but the effect is not directly related to the amount of pigment in the eye.