In The Netherlands, a national programme for the surveillance of zoonotic bacteria in farm animals has been operative since 1997. We describe the results of the surveillance of Salmonella spp. in flocks of laying hens and broilers and of Campylobacter spp. in broiler flocks in the period 1999-2002. The prevalence of Salmonella spp. in laying-hen flocks has significantly decreased from 21.1% in 1999 to 13.4% in 2002. This decreasing trend might indicate that the control measures taken by the poultry industry were effective. S. Enteritidis was the predominant serovar in laying hens accounting for one third of the positive flocks. Although prevalence estimates for Salmonella spp. in broiler flocks did not yield a significant decreasing trend in 1999-2002, a decrease in Salmonella prevalence to 11% was measured in 2002. During the study period, S. Paratyphi B var. Java emerged in broilers to become the predominant serovar in 2002 accounting for one third of the positive flocks. The prevalence of Campylobacter spp. in broiler flocks did not increase nor decrease continuously between 1999 and 2002, which roughly corresponds with the monitoring results from the poultry industry. In this period, the estimated flock prevalence roughly averaged around 20%, with C. jejuni being the predominant species. The approach of monitoring presented in this paper can serve as a blueprint for monitoring schemes in farm animal populations to be developed in the context of the EC Zoonoses Directive.