The parietal peritoneum was submitted to thermic stimulation in the course of peritoneoscopies, by touching it with the hot bulb of the instrument; all care was taken just to touch the wall, so that stimulation was practically confined to the serosa. All patients described the feeling as "stab sensation". They were able to localize the site of stimulation by pointing it with the finger, and that was easily checked because the light of the instrument could be seen through the abdominal wall in the darkened room. The characteristics of the elicited pain, specially with reference to the time-intensity curve (Lewis), correspond exactly to those described by Capps and Coleman, occasioned by mechanical stimulation. This "stab sensation" is well known by physicians because of its frequent occurence in pathologic envolvement of the parietal pleura and peritoneum. In contrast to Lewis' concept, according to which the time-intensity curve of pain would vary with the mode of stimulation, we find that the parietal peritoneum responds always in the same way regardless of the mode of stimulation, which agrees with clinical experience. The stab sensation aroused in the parietal peritoneum should thus be considered as a stereotyped reaction of predilective nature.