This paper measures the cost of implementing biosecurity on broiler and layer farms in Bali. Farmer investment in biosecurity is analysed to determine if there is any difference in the implementation of biosecurity between broiler and layer farms. Data is taken from a survey of 60 layer and 60 broiler smallholder farmers in Bali in 2009. While secure boundary fencing and farm gate locks are more common on layer farms, broiler producers are more likely to have a footbaths at the shed door. In this analysis, biosecurity investments include the quality of fencing and gates, presence of locks on gates, management changes required to minimise staff and visitor movement onto and in the farm, costs of minimising vehicle entry, use of vaccination and disinfectant, chlorination of water and quality of the chicken shed. Defining the relationships between present investment decisions and farm type, size and mortality rates will provide useful information to decision makers concerning the cost-effective levels of biosecurity that should be adopted by smallholder farmers in Bali. In Bali, decision makers are not only the individual farmers but also the government and private companies.