c-Kit immunopositive cells are considered to be pacemakers and/or mediators of neurotransmission in the gastrointestinal tract. They also correspond to the interstitial cells of Cajal (ICs) in mice. The normal distribution of c-Kit positive cells and their relation to ICs in the human gastrointestinal tract remain unclear. In this study we examine the distribution of c-Kit positive cells and their ultrastructure in normal human tissue. We then classified them and examined their relationship to ICs. Thirty nine samples of gut from the esophagus to the sigmoid colon from humans (ranging in age from a 16 week old fetus to a 57 year old and without motility disorders), were processed for immunohistochemistry, electronmicroscopy and immuno-electronmicroscopy. c-Kit immunopositive cells were located in the external muscle from the lower esophagus to the sigmoid colon, wherever the external muscle was composed of smooth muscle cells, and they were classified morphologically into two groups. Cells in the first group were mainly spindle-shaped bipolar cells with few branches; these cells ran parallel to nearby smooth muscle. Ultrastructurally, they possessed many intermediate filaments and caveolae. The spindle-shaped cells were present in the esophagus, stomach and small intestine. The second group of cells were located only in the colon, and were multipolar or bipolar cells with numerous branches. Cells in the second group were also rich in caveolae and/or smooth endoplasmic reticulum, but intermediate filaments were not prominent. Although both groups of c-Kit immunopositive cells corresponded to ICs, some ICs in the human gut do not appear to express c-Kit immunoreactivity.