The present study investigates the role of articulatory and perceptual factors in the change from pre- to post-aspiration in two varieties of Andalusian Spanish. In an acoustic study, the influence of stop type, speaker age, and variety on the production of pre- and post-aspiration was analyzed in isolated words produced by 24 speakers of a Western and 24 of an Eastern variety, both divided into two age groups. The results confirmed previous findings of a sound change from pre- to post-aspiration in both varieties. Velar stops showed the longest, bilabials the shortest, and dental stops intermediate pre- and post-aspiration durations. The observed universal VOT- pattern was not found for younger Western Andalusian speakers who showed a particularly long VOT in /st/-sequences. A perception experiment with the same subjects as listeners showed that post-aspiration was used as a cue for distinguishing the minimal pair /pata/-/pasta/ by almost all listeners. Production-perception comparisons suggested a relationship between production and perception: subjects who produced long post-aspiration were also more sensitive to this cue. In sum, the results suggest that the sound change has first been actuated in the dental context, possibly due to a higher perceptual prominence of post-aspiration in this context, and that post-aspirated stops in Andalusian Spanish are on their way to being phonologized.