Three provinces in the western part of Java Island in Indonesia participated in the study: Jakarta, Banten, and West Java (Figure) . Eighteen districts in these provinces were selected on the basis of their proximity to the laboratory, high levels of avian infl uenza activity in farmed birds (Ministry of Agriculture, unpub. data), and high number of LBMs available for study (n = 300). The required sample size was 73 markets based on an estimated disease prevalence of 50% and a maximum error of 10% at 95% confi dence. We based our assumption that 50% of LBMs would be contaminated with AIV (H5N1) on results from a previous study in US LBMs in 2001 (12) . This study found that 60% of markets tested positive for AIV (H7N2) virus in areas in which the virus was endemic. To account for nonresponse, we increased the total sample size to 83 LBMs. We selected markets for inclusion in the study using systematic sampling. On the basis of a sampling frame of 300 markets, every fourth market (the sampling interval) was selected from a list of all the markets. A random numbers table was used to determine the starting point for selection of the 83 markets from the list. Diagnostic specimens and data were collected during October 2007-March 2008. These months have high rainfall and high AIV transmission according to data gathered during 2005-2007 about AIV (H5N1) outbreaks in farmed birds (Ministry of Agriculture, unpub. data).