Enterobacter sakazakii, a pathogen that can be found in powdered infant milk formula, can cause adverse health effects on infants. Using Vickrey auction, this study examines parents' willingness to pay (WTP) for a quality assurance label on powdered infant milk formula. The influence of ambiguity with the incidence rate information and provision of safe-handling information on WTP are also evaluated using three experimental treatments. Our findings generally imply that parents significantly value a quality assurance label. The mean price premium parents are willing to pay for the safer and quality assurance labelled powdered infant milk formula ranges from 61 to 133 Eurocents per 100 grams (53–116% of the base price per 100 grams) depending on the treatment. While no ambiguity effects are generally found, provision of safe-handling information significantly reduced WTP to 39–69 Eurocents per 100 grams depending on the treatment. Copyright © 2008 John Wiley & Sons, Ltd.