Studies on brucellosis were carried out to elucidate the epidemiology of the disease in Isfahan province, where Brucella melitensis is highly prevalent in animals and man. A positive milk ring test of 32% and 23% was found in unvaccinated goats and sheep respectively. Card and tube agglutination tests showed an infection rate of about 12% in sheep and goats and 42% in cattle. B. melitensis was isolated from 8% of 677 samples of fresh cheese examined.Of 1526 clinically suspected human cases, 476 showed laboratory evidence of brucellosis. Of these patients, 291 cases were from urban and 185 cases from rural areas. Cases from urban and rural areas were seen principally in the younger age groups. The median age of infection was 19.7 in urban and 15.7 in rural patients respectively. The infection was encountered mainly from April to August. This correlates with animal parturition and the greatest amount of sheep and goat milk production, which is introduced to the local market as fresh cheese. Raw dairy product consumption is the most probable way of Brucella transmission in urban patients. In rural areas, both dairy product consumption and contact with animals are sources of infection.