In the present work, we explore the perceptual bases of infants' spontaneous looking preferences among isoluminant chromatic stimuli (Bornstein, 1975). Three experiments were conducted. In Experiment 1, adult subjects made brightness matches between a white standard and each of six isoluminant chromatic stimuli. The classic variations of brightness with chromaticity were found. In Experiment 2, 12-week-old infants' spontaneous looking preferences were measured for white lights of different luminances. Preference increased with increasing luminance, suggesting that brightness differences are sufficient to create looking preferences among isochromatic stimuli. In Experiment 3, infants' preferences were tested for each of the six chromatic stimuli paired against white, at both isoluminance and (adult) isobrightness. All chromatic stimuli were preferred to white, and the pattern of preferences was similar for both isoluminance and isobrightness conditions. It is concluded that hue and/or saturation, rather than brightness, control infants' spontaneous looking preferences among chromatic stimuli.