Brood sizes of House Sparrows (Passer domesticus) were altered experimentally by adding nestlings in order to create broods of either seven or eight young, where naturally occurring broods consisted of from two to five nestlings. Unmanipulated broods served as controls in this examination of parental investment in nestling feeding and care. Feeding rates of both parents increased as the size of the brood enlarged, but the attention given each young in such nests did not increase accordingly. Rather, the number of parental visits per nestling was significantly lower in supernormal broods than in normal ones. Males rearing larger broods invested a greater amount of effort in the feeding of their young than did comparable males raising normal broods. Increases in male feeding activity through the nestling period were evident in males caring for supernormal broods, while males raising normal broods decreased their feeding efforts after the nestlings reached a few days in age. Females raising supernormal broods also increased their efforts to meet the increased demands of the enlarged broods. Nevertheless, a greater correlation between feeding rates and nestling age was observed than between feeding rates and brood type. House sparrows were able to raise larger than normal numbers of nestlings, but the increased demands placed upon both the young and the adults may have ultimately affected their reproductive capacities by altering their normal behavior patterns.