Twenty-five lines of the IRAN strain Anopheles stephensi, 32 of the MOYO INDOOR strain of Aedes aegypti and 37 of the MASAKA strain of Ae. aegypti were inbred by the single-pair, brother-sister mating technique. Two lines of the IRAN strain of An. stephensi were successfully carried through six generations of inbreeding, and five lines of the MOYO INDOOR strain and two lines of the MASAKA strain of Ae. aegypti were successfully carried through 10 generations of inbreeding. Four inbred strains derived from the MOYO INDOOR strain and two derived from the MASAKA strain were compared with respect to size, color pattern and life table characteristics. Each strain exhibited a distinctive and unique combination of deleterious and adaptive traits. Comparison of the inbred strains with the respective parent strains demonstrated reduced fitness in all of the inbred strains.