In February 2004, an HPAI virus was confirmed to have infected a flock of broiler chickens in Gonzales County, Texas. Subsequent epidemiologic investigation identified infected birds in 2 live-bird markets in the area of Houston, Tex; these markets had received birds from the index flock or birds that had been transported by the index flock manager. All infected premises were depopulated, cleaned, and disinfected. Disease surveillance standards were established to assess the potential for spread of this virus from the index flock. Surveillance testing in commercial and noncommercial poultry operations revealed no area spread of virus from the index flock.