Gallbladder carcinoma was induced in hamsters by inserting methylcholanthrene beeswax pellets into the gallbladder lumen. The histogenesis and mode of development of the cancer was studied. The mode of development was classified into four; the infiltrative, the polypoid, the para-adenoma, and the mixed type. Twenty-one gallbladder carcinoma included six of the infiltrative type, seven of the polypoid type, three of the para-adenoma type (each case was accompanied by the infiltrative type), and eight of the mixed type (containing three of the infiltrative plus the para-adenoma type, and five of the infiltrative plus the polypoid type). Concerning histogenesis, the infiltrative type developed as de novo cancer. The polypoid and the para-adenoma type developed from adenomatous hyperplasia or adenoma.