Human infants' thresholds for detecting 10 degrees diameter 50 and 1000 msec stimuli in the dark adapted condition and in the presence of steady red backgrounds were determined using a preferential looking method. Dark adapted sensitivity and the slope of the linear portion of the increment threshold function increased with age. The slope was 0.5 at 4 weeks, but by 10 weeks it was not different from the adult value (approximately 1.0). At all ages the eigengrau was approximately the same as that of adults (-2.3 log scot. td). These results suggest that visual mechanisms involved in detection of flashes and adaptation to steady background lights mature postnatally.