● Two separate groups of Dutch microbiologists led clandestine efforts to produce antibiotics while the country was occupied during World War II. ● In one of these efforts, J.V. Köningsberger and Abraham van Luyk at the Botanical Laboratory in Utrecht tested antibiotics produced by Penicillium expansum on animals and humans. ● Although hampered by wartime censorship, this Dutch group benefitted from information on penicillin from an unusual source—namely, a leaflet that British Royal Air Force (RAF) fliers dropped over Holland. ● The group in Utrecht laboured under conditions of severe deprivation, but despite their best efforts their work came to an abrupt end in August 1944 when gas and electricity supplies collapsed.