We introduced home drinking water disinfection and handwashing with soap in Karachi squatter settlements to evaluate their effect on diarrhea. In April 2000, 150 households received soap, 76 received dilute bleach and a water storage vessel, and 76 were enrolled as controls. In 2000, among households wealthy enough to own a refrigerator, children in households that received bleach and a vessel had a 73% lower incidence of diarrhea than controls; those that received soap had a 56% lower incidence. There was no reduction in diarrhea in intervention households without a refrigerator. In 2001, households that received bleach and a vessel had a 71% lower incidence of diarrhea and children in households that received soap had a 35% lower incidence than controls. In 2001, the interventions were equally effective in households that had a refrigerator and those that did not. Both of these home-based interventions were ultimately effective in preventing diarrhea, but only households of slightly higher socioeconomic status changed their behavior quickly enough to benefit during the first summer.