Abstract: Antagonists for use in commercial biocontrol products have to fulfil many differentrequirements. Besides being active control agents against the specific targeted plant pathogens,they must be safe and cost effective. The development of new biocontrol products starts withscreening programs including hundreds or thousands of candidates. For commercial use,important criteria are market size, efficacy, ecological characteristics, production costs, safety,environmental risks and protection of intellectual property rights. A stepwise screeningconsidering these very different aspects is proposed.