Aim: To study the possible role of somatostatin in analgesia. Methods: In situ hybridization (ISHH) and image processing were used to study the change of somatostatin (SOM) mRNA level in periaqueductal gray matter (PAG) of rats in the normal group, noxious stimulation group, simple acupuncture group and electroacupuncture analgesia group (EA). Results: In normal group, SOM mRNA positive cells with intense hybridization signal were mainly oval and concentrated principally in ventromedial, ventrolateral subnuclei of PAG. An increase of SOM mRNA positive cells was seen in noxious stimulation group and simple acupuncture group comparing with the normal group. In EA group the number of SOM mRNA positive cells increased more than any other groups. Conclusion: 1. SOM may take part in pain modulation. 2. SOM may play a role in EA.