We measured the two-week household-level economic impact of insecticide (permethrin)-treated bed nets (ITNs) used to prevent malaria among children less than five years of age in Asembo, Kenya. The ITNs induced a two-week reduction of 15 Kenyan shillings (KSH) (0.25 U.S. dollars; P < 0.0001) in health care expenditures, but a statistically insignificant 0.5 day (P = 0.280) reduction in household time lost due to caring for sick children. The equivalent annual threshold cost was estimated at 6.50 U.S. dollars (95% confidence interval = 3.12-9.86). If the actual purchase price and maintenance costs of ITNs were greater than this threshold, then households would pay more than they would save (and vice-versa). Both seasonal effects and number of children per household had larger impacts than ITNs on health care expenditures and time lost from household activities. Health care expenditures by a household without ITNs and one child were only 32 KSH per two weeks (0.50 U.S. dollars; P = 0.002), leaving little opportunity for household-level, ITN-induced direct savings. The widespread adoption of the ITNs will therefore probably require a subsidy.