Histamine content of the intestine of young female Swiss albino mice experimentally infected per os with low (500) and high (2000) doses of Ancylostoma caninum larvae was studied. The histamine level increased in both the experimental groups reaching peak values on the 16th day post infection in animals inoculated with a dose of 500 larvae and on the 30th day post infection in animals inoculated with 2000 larvae; the histamine content was 2.5 times higher in the former and 4 times higher in the latter than that in the uninfected controls.