Experiments were made in which Aedes aegypti mosquitoes fed on a dog infected with Dirofilaria immitis, in order to determine the distribution pattern of microfilariae (Mf) in the dog's periphery blood and the number of Mf taken by the mosquitoes. Mosquitoes fed on an anesthetized dog at some 50 shaved skin spots and they were weighed immediately before and after feeding. This enabled us to examine not only the Mf number taken by each mosquito but also the Mf intake density in terms of Mf number per mg of blood. The Mf intake density showed a wide variation at the different parts of the dog's body, and the frequencies of Mf showed uneven distributions which were fitted best by the negative binomial. Significant differences were detected in the Mf intake density at different parts of the skin, but these differences were concluded as a non-consistent result because a similar result was not reproduced in the next experiment. It was presumed that not only the Mf number per mosquito but also the Mf intake density increased as the blood intake by the mosquitoes increased. This increase of both the Mf number per mosquito and the Mf intake density was also supported by another experiment in which mosquitoes were fed at the same skin spots consecutively one after another.