The cells containing 5-hydroxytryptamine (5-HT) in the antrum of the SD rat's stomach were demonstrated by means of Sternberger's PAP immunohistochemical method and quantitative analysis were performed by means of Weibel's stereological method. The results were as follow: The 5-HT immunoreactive cells in the antrum of the rat's stomach were found only in the surface epithelium and the glandular epithelium of the mucosa. The volume density (V_v) was 0.0038?0.0004, the surface density (N_A) was 42.86+3.20 cells/mm~2 and the numerical density (N_v) was 2627.11?200.42 cells/mm~3. The distribution of 5-HT reactive cells showed an obvious regional difference. From the lesser curvature to the greater curvature of stomach, the cell density decreased gradually. The cell density was the highest in the lesser curvature: N_A was 59.96?3.48 cells/mm~2, Nv was 3729.23?216.89 cells/mm~3; and was second high in the two side walls: N_A was 42.39?3.48 cells/mm~2, Nv was 2647.18+216.57 cells/mm~3; and was lowest in the greater curvature: N_A was 29.39? 4.49 cells/mm~2, N_v was 1843.00?280.09 cells/mm~3. Most of the 5-HT immunoreaclive cells were found in the basal third section of the mucosa and the cell density was the highest. N_A was 92.33?6.92 cell/mm~2,N_v was 5336.28?410.22 cells/ mm~3; in the middle one third of the mucosa, the cell density came to next: N_A was 27.69?2.38 cells/mm~2, N_A was 1708.68?146.65 cells/mm~3; and in the superficial third section of the mucosa, the cell density was the lowest: N_A was 7.29?0.53 cells/mm~2, N_v was 457.00?35.44 cells/mm~3. In addition, a detailed observation on the morphology of the 5-HT immunoreactive cells was also undertaken.