We examined the effect of stimulus complexity and frequency on infants' attention responses during an auditory habituation procedure. Five stimuli of different complexity and frequency were presented repeatedly to 80 5-month-old infants. Quicker attention-getting and longer attention-holding responses were obtained with the more complex stimuli. Furthermore, a progressive decrease in attention-holding, but not in attention-getting, was observed across trials. The findings are similar to those well established in the visual modality [e.g., Cohen et al. (Child Dev. 1975; 46: 611); Slater et al. (Br. J. Dev. Psychol. 1984; 2: 287)] showing that auditory complexity is an important variable in attracting and maintaining infant attention, and that only attention-holding is subject to habituation. Although the complex stimulus contained higher frequencies than the simple or intermediate stimuli, our results further showed that stimulus frequency alone had no significant effect on attention-getting or attention-holding, which strengthens our claim that complexity preference during habituation can be generalized to the auditory modality. Copyright © 2004 John Wiley & Sons, Ltd.