To determine whether physiological differences exist between primary (swallow-induced) and secondary (distension-induced) peristalsis in humans, 10 healthy male volunteers underwent esophageal manometry on 2 consecutive days using a perfused intraluminal catheter system that incorporated a latex balloon. Initially the catheter was positioned so that the balloon was centered 16 cm above the lower esophageal sphincter (LES), and intraluminal pressures were recorded 21, 11, 6, and 1 cm above the LES. After a series of wet swallows, dry swallows, and balloon distensions, the catheter was repositioned so that the balloon was 6 cm above the LES and pressures were recorded 1 and 11 cm above the LES. A series of balloon distensions were repeated in this position, and the subject was then given either atropine (10 micrograms/kg iv) or placebo in a double-blind randomized fashion (on consecutive days). The protocol was then repeated in reverse order. Distension-induced responses aboral to the balloon with the balloon located 16 cm above the LES were 1) of lower amplitude, 2) more often nonperistaltic, and 3) less atropine sensitive than swallow-induced contractions at comparable sites. With the balloon located distally (6 cm above LES) contractions induced at the 11-cm site (i.e., orad to the balloon) were much more atropine sensitive than contractions induced at the same site when the balloon was located proximally (i.e., 16 cm above LES). These data suggest that, contrary to previous reports, secondary peristalsis differs significantly from primary peristalsis. Furthermore, atropine differentially effects these two types of peristalsis, suggesting that the neural pathways involved are dissimilar.