The effect of stimulus duration on the b-wave and psychophysical responses of dark-adapted 10-week-old infants and adult control subjects is reported. Both infant and adult b-wave sensitivities vary with stimulus duration, show summation for brief duration stimuli, critical durations estimated at 88–155 msec, and little variation in sensitivity for longer durations. There are, however, substantial differences between the infant and adult psychophysical temporal summation functions. The infant function is described by a straight line, slope about −0.5, across all flash durations while adults show summation at durations < 100 msec and critical durations of 136 to 151 msec. Adult, but not infant, b-wave integration times and b-wave rise and fall times show duration-dependent changes. Thus, both ERG and psychophysical measures demonstrate immaturities in the rod mediated function of the infant retina.