In order to investigate how the ganglia in ganglionated plexus were distributed throughout the overall region of the gallbladder, the gallbladder was dissected from guinea-pig and washed with Krebs solution via the cystic duct. This gallbladder was distended with 2 ml of the mixed solution of OsO4 and ZnI2 injected with a syringe via the cystic duct and the cystic duct was immediately tied with a thread. The gallbladder was placed in excess of the mixed solution for 7-10 hours. The gallbladder was longitudinally divided into two approximately equal parts and each was prepared for microscopic investigation. The one preparation was the ventral side of the gallbladder and the other preparation was its dorsal side. These preparations were viewed through a photomicroscope. The obtained results were as follows: 1. Ganglia which involved several nerve cells were observed. Ganglia and nerve bundles connecting the fellow ganglia formed an irregular network, that is, the so-called ganglionated plexus. These nerve bundles were connected with the perivascular nerves which ran parallel to and around blood vessels in several places of the wall of the gallbladder. 2. Ganglia were full of variety in size and shape. That is to say, the shape of ganglia is arranged in various patterns such as oval, spherical, triangular, square and so on. When the size of ganglia were shown by surface area of ganglia which were viewed within the sweep of photomicroscope, the size of ganglia were divided into three large groups, the small ganglia in the range of 1,400 microns2-3,500 microns 2, the large ganglia in the range of 3,500 microns2-10,000 microns2 and the extra-large ganglia in the range of 10,000 microns2-38,000 microns2. Per one gallbladder, 240 +/- 41 (n = 3) small ganglia, 263 +/- 28 (n = 3) large ganglia and 8 +/- 1 (n = 3) extra-large ganglia were found. And these ganglia were irregularly scattered all over the wall of gallbladder. Small ganglia were found more numerous than large ganglia in the cervical portion of the gallbladder. On the other hand, small ones were slightly fewer than large ganglia in the remainder portion of the gallbladder. 3. The ganglionated plexus contained 511 +/- 69 (n = 3) ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)