In Experiment I, rats 13-35 days of age were presented with acoustic startle stimuli in conjunction with light flashes or noise bursts at 4-320 msec lead times. Inhibition of the startle reflex by leading noise bursts was present on Days 13-15, whereas light flashes were not effective until Days 21-23. In Experiment II, 3 intensities of noise and 3 intensities of light preceded the reflex-eliciting stimuli on Days 16 and 35. All intensities of noise were effective on Day 16, whereas no visual stimuli were. On Day 35, all stimuli were effective. These data reveal that intrinsic visual structures and/or connections between these structures and reflex-control mechanisms mature relatively late in the rat.